[
    {
        "text": "Quantum Hall States in Graphene from Strain-Induced Nonuniform Magnetic\n  Fields: We examine strain-induced quantized Landau levels in graphene. Specifically,\narc-bend strains are found to cause nonuniform pseudomagnetic fields. Using an\neffective Dirac model which describes the low-energy physics around the nodal\npoints, we show that several of the key qualitative properties of graphene in a\nstrain-induced pseudomagnetic field are different compared to the case of an\nexternally applied physical magnetic field. We discuss how using different\nstrain strengths allows us to spatially separate the two components of the\npseudospinor on the different sublattices of graphene. These results are\nchecked against a tight-binding calculation on the graphene honeycomb lattice,\nwhich is found to exhibit all the features described. Furthermore, we find that\nintroducing a Hubbard repulsion on the mean-field level induces a measurable\npolarization difference between the A and the B sublattices, which provides an\nindependent experimental test of the theory presented here.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Euler equation of the optimal trajectory for the fastest magnetization\n  reversal of nano-magnetic structures: Based on the modified Landau-Lifshitz-Gilbert equation for an arbitrary\nStoner particle under an external magnetic field and a spin-polarized electric\ncurrent, differential equations for the optimal reversal trajectory, along\nwhich the magnetization reversal is the fastest one among all possible reversal\nroutes, are obtained. We show that this is a Euler-Lagrange problem with\nconstrains. The Euler equation of the optimal trajectory is useful in designing\na magnetic field pulse and/or a polarized electric current pulse in\nmagnetization reversal for two reasons. 1) It is straightforward to obtain the\nsolution of the Euler equation, at least numerically, for a given magnetic\nnano-structure characterized by its magnetic anisotropy energy. 2) After\nobtaining the optimal reversal trajectory for a given magnetic nano-structure,\nfinding a proper field/current pulse is an algebraic problem instead of the\noriginal nonlinear differential equation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "All Spin Logic device with inbuilt Non-Reciprocity: The need for low power alternatives to digital electronic circuits has led to\nincreasing interest in logic devices where information is stored in\nnanomagnets. This includes both nanomagnetic logic (NML) where information is\ncommunicated through magnetic fields of nanomagnets and all-spin logic (ASL)\nwhere information is communicated through spin currents. A key feature needed\nfor logic implementation is non-reciprocity, whereby the output is switched\naccording to the input but not the other way around, thus providing directed\ninformation transfer. The objective of this paper is to draw attention to\npossible ASL-based schemes that utilize the physics of spin-torque to build in\nnon-reciprocity similar to transistors that could allow logic implementation\nwithout the need for special clocking schemes. We use an experimentally\nbenchmarked coupled spin-transport/ magnetization-dynamics model to show that a\nsuitably engineered single ASL unit indeed switches in a non-reciprocal manner.\nWe then present heuristic arguments explaining the origin of this directed\ninformation transfer. Finally we present simulations showing that individual\nASL devices with inbuilt directionality can be cascaded to construct circuits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamic screening of quasiparticles in WS$_2$ monolayers: We unravel the influence of quasiparticle screening in the non-equilibrium\nexciton dynamics of monolayer WS$_2$. We report pump photon energy-dependent\nexciton blue and red-shifts from time-resolved-reflectance contrast\nmeasurements. Based on a phenomenological model, we isolate the effective\nimpact of excitons and free carriers on the renormalization of the quasi-free\nparticle band gap, exciton binding energy and linewidth broadening. By this,\nour work does not only provide a comprehensive picture of the competing\nphenomena governing the exciton dynamics in WS$_2$ upon photoexcitation, but\nalso demonstrates that exciton and carrier contributions to dynamic screening\nof the Coulomb interaction differ significantly.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spaser as Nanoscale Quantum Generator and Ultrafast Amplifier: Nanoplasmonics has recently experienced explosive development with many novel\nideas and dramatic achievements in both fundamentals and applications. The\nspaser has been predicted and observed experimentally as an active element --\ngenerator of coherent local fields. Even greater progress will be achieved if\nthe spaser could function as a ultrafast nanoamplifier -- an optical\ncounterpart of the MOSFET (metal-oxide-semiconductor field-effect transistor).\nA formidable problem with this is that the spaser has the inherent feedback\ncausing quantum generation of nanolocalized surface plasmons and saturation and\nconsequent elimination of the net gain, making it unsuitable for amplification.\nWe have overcome this inherent problem and shown that the spaser can perform\nfunctions of an ultrafast nanoamplifier in two modes: transient and bistable.\nOn the basis of quantum density matrix (optical Bloch) equations we have shown\nthat the spaser amplifies with gain greater than 50, the switching time less or\non the order of 100 fs (potentially, 10 fs). This prospective spaser technology\nwill further broaden both fundamental and applied horizons of nanoscience, in\nparticular, enabling ultrafast microprocessors working at 10 to 100 THz clock\nspeed. Other prospective applications are in ultrasensing, ultradense and\nultrafast information storage, and biomedicine. The spasers are based on metals\nand, in contrast to semiconductors, are highly resistive to ionizing radiation,\nhigh temperatures, microwave radiation, and other adverse environments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Circulating persistent current and induced magnetic field in a fractal\n  network: We present the overall conductance as well as the circulating currents in\nindividual loops of a Sierpinski gasket (SPG) as we apply bias voltage via the\nside attached electrodes. SPG being a self-similar structure, its manifestation\non loop currents and magnetic fields are examined in various generations of\nthis fractal and it has been observed that for a given configuration of the\nelectrodes, the physical quantities exhibit certain regularity as we go from\none generation to another. Also a notable feature is the introduction of\nanisotropy in hopping causes an increase in magnitude of overall transport\ncurrent. These features are a subject of interest in this article.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ellipsometry studies of Si/Ge superlattices with embedded Ge dots: In this paper, we present an analysis for treating the spectroscopic\nellipsometry response of Si/Ge superlattices (SL) with embedded Ge dots.\nSpectroscopic ellipsometry (SE) measurement at room temperature was used to\ninvestigate optical and electronic properties of Si/Ge SL which were grown on\nsilicon (Si) wafers having <111> crystallographic orientation. The results of\nthe SE analysis between 200 nm and 1000 nm indicate that the SL system can\neffectively be described using interdiffusion/intermixing model by assuming a\nmulticrystalline Si and Si1-xGex intermixing layers. The electronic transitions\ndeduced from analysis reveal Si, Ge and alloying related critical energy\npoints.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Conductance of a quantum point contact based on spin-density-functional\n  theory: We present full quantum mechanical conductance calculations of a quantum\npoint contact (QPC) performed in the framework of the density functional theory\n(DFT) in the local spin-density approximation (LDA). We show that a\nspin-degeneracy of the conductance channels is lifted and the total conductance\nexhibits a broad plateau-like feature at 0.5*2e^{2}/h. The lifting of the\nspin-degeneracy is a generic feature of all studied QPC structures (both very\nshort and very long ones; with the lengths in the range 40<l<500 nm). The\ncalculated conductance also shows a hysteresis for forward- and backward sweeps\nof the gate voltage. These features in the conductance can be traced to the\nformation of weakly coupled quasi-bound states (magnetic impurities) inside the\nQPC (also predicted in previous DFT-based studies). A comparison of obtained\nresults with the experimental data shows however, that while the spin-DFT based\n\"first-principle\" calculations exhibits the spin polarization in the QPC, the\ncalculated conductance clearly does not reproduce the 0.7 anomaly observed in\nalmost all QPCs of various geometries. We critically examine major features of\nthe standard DFT-based approach to the conductance calculations and argue that\nits inability to reproduce the 0.7 anomaly might be related to the infamous\nderivative discontinuity problem of the DFT leading to spurious\nself-interaction errors not corrected in the standard LDA. Our results indicate\nthat the formation of the magnetic impurities in the QPC might be an artefact\nof the LDA when localization of charge is expected to occur. We thus argue that\nan accurate description of the QPC structure would require approaches that go\nbeyond the standard DFT+LDA schemes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Order from Disorder in Graphene Quantum Hall Ferromagnet: Valley-polarized quantum Hall states in graphene are described by a\nHeisenberg O(3) ferromagnet model, with the ordering type controlled by the\nstrength and sign of valley anisotropy. A mechanism resulting from electron\ncoupling to strain-induced gauge field, giving leading contribution to the\nanisotropy, is described in terms of an effective random magnetic field aligned\nwith the ferromagnet z axis. We argue that such random field stabilizes the XY\nferromagnet state, which is a coherent equal-weight mixture of the $K$ and $K'$\nvalley states. Other implications such as the Berezinskii-Kosterlitz-Thouless\nordering transition and topological defects with half-integer charge are\ndiscussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Intrinsic Spin Swapping: Here, we study diffusive spin transport in two dimensions and demonstrate\nthat an intrinsic analog to a previously predicted extrinsic spin swapping\neffect, where the spin polarization and the direction of flow are interchanged\ndue to spin-orbit coupling at extrinsic impurities, can be induced by intrinsic\n(Rashba) spin-orbit coupling. The resulting accumulation of intrinsically\nspin-swapped polarizations is shown to be much larger than for the extrinsic\neffect. Intrinsic spin swapping is particularly strong when the system\ndimensions exceed the spin-orbit precession length and the generated transverse\nspin currents are of the order of the injected primary spin currents. In\ncontrast, spin accumulations and spin currents caused by extrinsic spin\nswapping are proportional to the spin-orbit coupling. We present numerical and\nanalytical results for the secondary spin currents and accumulations generated\nby intrinsic spin swapping, and we derive analytic expressions for the induced\nspin accumulation at the edges of a narrow strip, where a long-range\npropagation of spin polarizations takes place.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Local density of states in disordered graphene: We study two lattice models, the honeycomb lattice (HCL) and a special square\nlattice (SQL), both reducing to the Dirac equation in the continuum limit. In\nthe presence of disorder (gaussian potential disorder and random vector\npotential), we investigate the behaviour of the density of states (DOS)\nnumerically and analytically. While an upper bound can be derived for the DOS\non the SQL at the Dirac point, which is also confirmed by numerical\ncalculations, no such upper limit exists for the HCL in the presence of random\nvector potential. A careful investigation of the lowest eigenvalues indeed\nindicate, that the DOS can possibly be divergent at the Dirac point on the HCL.\nIn spite of sharing a common continuum limit, these lattice models exhibit\ndifferent behaviour.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum interference and contact effects in dangling bond loops on\n  H-Si(100) surfaces: We perform electronic structure and quantum transport studies of dangling\nbond loops created on H-passivated Si(100) surfaces and connected to carbon\nnanoribbon leads. We model loops with straight and zigzag topologies as well as\nwith varying lenght with an efficient density-functional based tight-binding\nelectronic structure approach (DFTB) . Varying the length of the loop or the\nlead coupling position we induce the drastic change in the transmission due to\nthe electron interference. Depending if the constructive or destructive\ninterference within the loop takes place we can noticeably change transport\nproperties by few orders of magnitude. These results propose a way to engineer\nthe closed electronically driven nanocircuits with high transport properties\nand exploit the interference effects in order to control them.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Phase biasing of a Josephson junction using Rashba-Edelstein effect: Manifestation of orbital coupling of spin degree of freedom in condensed\nmatter systems has opened up a new dimension for the field of spintronics. The\nmost appealing aspect of the spin-orbit coupling is the apparent Magnus force\nsensed by a spin system which locks the Fermi momentum with electron spin in a\nfascinating manner. In the current carrying state, the resulting macroscopic\nspin polarization becomes directly accessible in the form of spin current or\nspin density. At a Rashba interface, for example, a charge current shifts the\nspin-locked Fermi surface, leading to a non-equilibrium spin density at the\ninterface, commonly known as the Rashba-Edelstein effect. Since the\nRashba-Edelstein effect is an intrinsically interface property, direct\ndetection of the spin moment is harder to set-up. Here we demonstrate that a\nsimple planar Josephson Junction geometry, realized by placing two closely\nspaced superconducting electrodes on such a Rashba interface, allows a direct\nestimation of strength of the non-equilibrium spin moment. Measurements of\nFraunhofer patterns of Nb-(Pt/Cu)-Nb planar Josephson junctions in a\nperpendicular magnetic field showed a shift of the center of the Fraunhofer\npattern to a non-zero field value. By performing extensive control\nmeasurements, we argue that the screening currents in the junction effectively\nlock the external field with the spin moment of the Rashba-Edelstein effect\ninduced spin-density, leading to the observed shift in the Fraunhofer patterns.\nThis simple experiment offers a fresh perspective on direct detection of spin\npolarization induced by various spin-orbit effects. Very interestingly, this\ndevice platform also offers the possibility of retaining a controllable phase\nat zero field in the junction without using any magnetic material, and thereby\nuseful as phase batteries for superconducting quantum circuits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bulk-edge correspondence of Stiefel-Whitney and Euler insulators through\n  the entanglement spectrum and cutting procedure: We propose an unconventional bulk-edge correspondence for two-dimensional\nStiefel-Whitney insulators and Euler insulators, which are topological\ninsulators protected by the $PT$ symmetry. We find that, although the energy\nspectrum under the open boundary condition is generally gapped, the\nentanglement spectrum is gapless when the Stiefel-Whitney or Euler class is\nnonzero. The robustness of the gapless spectrum for Stiefel-Whitney insulator\ncan be understood through an emergent anti-unitary particle-hole symmetry. For\nthe Euler insulators, we propose a conjecture, which is supported by our\nnumerical calculation, that the Euler class is equal to the number of crossing\nin the entanglement spectrum, taking into account the degree of the crossings.\nWe also discuss that these crossings of the entanglement spectrum are related\nto the gap closing points in the cutting procedure, which is the energy\nspectrum as the magnitude of the boundary hopping is varied.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Origin of the hysteresis in bilayer 2D systems in the quantum Hall\n  regime: The hysteresis observed in the magnetoresistance of bilayer 2D systems in the\nquantum Hall regime is generally attributed to the long time constant for\ncharge transfer between the 2D systems due to the very low conductivity of the\nquantum Hall bulk states. We report electrometry measurements of a bilayer 2D\nsystem that demonstrate that the hysteresis is instead due to non-equilibrium\ninduced current. This finding is consistent with magnetometry and electrometry\nmeasurements of single 2D systems, and has important ramifications for\nunderstanding hysteresis in bilayer 2D systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Observation of Hysteretic Transport Due to Dynamic Nuclear Spin\n  Polarization in a GaAs Lateral Double Quantum Dot: We report a new transport feature in a GaAs lateral double quantum dot that\nemerges only for magnetic field sweeps and shows hysteresis due to dynamic\nnuclear spin polarization (DNP). This DNP signal appears in the Coulomb\nblockade regime by virtue of the finite inter-dot tunnel coupling and\noriginates from the crossing between ground levels of the spin triplet and\nsinglet extensively used for nuclear spin manipulations in pulsed gate\nexperiments. The unexpectedly large signal intensity is suggestive of\nunbalanced DNP between the two dots, which opens up the possibility of\ncontrolling electron and nuclear spin states via DC transport.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Entangling electrons by splitting Cooper pairs: Two-particle conductance\n  resonance and time coincidence measurements: Entanglement, being at the heart of the Einstein-Podolsky-Rosen (EPR)\nparadox, is a necessary ingredient in processing quantum information. Cooper\npairs in superconductors - being composites of two fully entangled electrons -\ncan be split adiabatically, thus forming entangled electrons. We fabricated\nsuch electron splitter by contacting an aluminum superconductor strip at the\ncenter of a suspended InAs nanowire; terminated at both ends with two normal\nmetallic drains. Intercepting each half of the nanowire by gate - induced\nCoulomb blockaded quantum dot strongly impeded the flow of Cooper pairs due to\nlarge charging energy, while still permitting passage of single electrons.\nHere, we provide conclusive evidence of extremely high efficiency Cooper pairs\nsplitting via observing positive average (conductance) and time (shot noise)\ncorrelations of the split electrons in the two opposite drains of the nanowire.\nMoreover, The actual charge of the injected quasiparticles was verified by shot\nnoise measurements.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anyonic order parameters for discrete gauge theories on the lattice: We present a new family of gauge invariant non-local order parameters for\n(non-abelian) discrete gauge theories on a Euclidean lattice, which are in\none-to-one correspondence with the excitation spectrum that follows from the\nrepresentation theory of the quantum double D(H) of the finite group H.\n  These combine magnetic flux-sector labeled by a conjugacy class with an\nelectric representation of the centralizer subgroup that commutes with the\nflux. In particular cases like the trivial class for magnetic flux, or the\ntrivial irrep for electric charge, these order parameters reduce to the\nfamiliar Wilson and the 't Hooft operators respectively. It is pointed out that\nthese novel operators are crucial for probing the phase structure of a class of\ndiscrete lattice models we define, using Monte Carlo simulations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strain engineering the charged-impurity-limited carrier mobility in\n  phosphorene: We investigate, based on the tight-binding model and in the linear\ndeformation regime, the strain dependence of the electronic band structure of\nphosphorene, exposed to a uniaxial strain in one of its principle directions,\nthe normal, the armchair and the zigzag directions. We show that the electronic\nband structure of strained phosphorene, for experimentally accessible carrier\ndensities and uniaxial strains, is well described by a strain-dependent\ndecoupled electron-hole Hamiltonian. Then, employing the decoupled Hamiltonian,\nwe consider the strain dependence of the charged-impurity-limited carrier\nmobility in phosphorene, for both types of carrier, arbitrary carrier density\nand in both armchair and zigzag directions. We show that a uniaxial tensile\n(compressive) strain in the normal direction enhances (weakens) the anisotropy\nof the carrier mobility, while a uniaxial strain in the zigzag direction acts\ninversely. Moreover applying a uniaxial strain in the armchair direction is\nshown to be ineffective on the anisotropy of the carrier mobility. These will\nbe explained based on the effect of the strain on the carrier effective mass.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Broadband terahertz probes of anisotropic magnetoresistance disentangle\n  extrinsic and intrinsic contributions: Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of\nmagnetic order in contemporary spintronics research. Its origins are usually\nascribed to extrinsic effects (i.e. spin-dependent electron scattering),\nwhereas intrinsic (i.e. scattering-independent) contributions are neglected.\nHere, we measure AMR of polycrystalline thin films of the standard ferromagnets\nCo, Ni, Ni81Fe19 and Ni50Fe50 over the frequency range from DC to 28 THz. The\nlarge bandwidth covers the regimes of both diffusive and ballistic intraband\nelectron transport and, thus, allows us to separate extrinsic and intrinsic AMR\ncomponents. Analysis of the THz response based on Boltzmann transport theory\nreveals that the AMR of the Ni, Ni81Fe19 and Ni50Fe50 samples is of\npredominantly extrinsic nature. However, the Co thin film exhibits a sizeable\nintrinsic AMR contribution, which is constant up to 28 THz and amounts to more\nthan 2/3 of the DC AMR contrast of 1%. These features are attributed to the\nhexagonal structure of the Co crystallites. They are interesting for\napplications in terahertz spintronics and terahertz photonics. Our results show\nthat broadband terahertz electromagnetic pulses provide new and contact-free\ninsights into magneto-transport phenomena of standard magnetic thin films on\nultrafast time scales.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Validity of the Lowest Landau Level Approximation for Rotating Bose\n  Gases: The energy spectrum for an ultracold rotating Bose gas in a harmonic trap is\ncalculated exactly for small systems, allowing the atoms to occupy several\nLandau levels. Two vortex-like states and two strongly correlated states (the\nPfaffian and Laughlin) are considered in detail. In particular, their critical\nrotation frequencies and energy gaps are determined as a function of particle\nnumber, interaction strength, and the number of Landau levels occupied (up to\nthree). For the vortex-like states, the Lowest Landau level (LLL) approximation\nis justified only if the interaction strength decreases with the number of\nparticles; nevertheless, the constant of proportionality increases rapidly with\nthe angular momentum per particle. For the strongly correlated states, however,\nthe interaction strength can increase with particle number without violating\nthe LLL condition. The results suggest that in large systems, the Pfaffian and\nLaughlin states might be stabilized at rotation frequencies below the\ncentrifugal limit for sufficiently large interaction strengths, with energy\ngaps a significant fraction of the trap energy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Frequency-Dependent Current Noise through Quantum-Dot Spin Valves: We study frequency-dependent current noise through a single-level quantum dot\nconnected to ferromagnetic leads with non-collinear magnetization. We propose\nto use the frequency-dependent Fano factor as a tool to detect single-spin\ndynamics in the quantum dot. Spin precession due to an external magnetic and/or\na many-body exchange field affects the Fano factor of the system in two ways.\nFirst, the tendency towards spin-selective bunching of the transmitted\nelectrons is suppressed, which gives rise to a reduction of the low-frequency\nnoise. Second, the noise spectrum displays a resonance at the Larmor frequency,\nwhose lineshape depends on the relative angle of the leads' magnetizations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The two dimensional local density of states of a Topological Insulator\n  with an edge dislocation: We investigate the effect of a crystal edge dislocation on the metallic\nsurface of a Topological Insulator. The edge dislocation gives rise to torsion\nwhich the electrons experience as a spin connection. As a result the electrons\npropagate along confined two dimensional regions and circular contours. Due to\nthe edge dislocations the parity symmetry is violated resulting in a current\nmeasured by the in-plane component of the spin on the surface.\n  The tunneling density of states for Burger vectors in the $y$ direction is\nmaximal along the $x$ direction. The evidence of the enhanced tunneling density\nof states can be verified with the help of the scanning tunneling technique.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Temperature dependence of spin polarization in ferromagnetic metals\n  using lateral spin valves: A high reproducibility in the performance of cobalt/copper and\npermalloy/copper lateral spin valves with transparent contacts is obtained by\noptimizing the interface quality and the purity of copper. This allows us to\nstudy comprehensively the spin injection properties of both ferromagnetic\nmaterials, as well as the spin transport properties of copper, which are not\naffected by the used ferromagnetic material, leading to long spin diffusion\nlengths. Spin polarizations of permalloy and cobalt are obtained as a function\nof temperature. Analysis of the temperature dependence of both the spin\npolarization and conductivity of permalloy using the standard two-channel model\nfor ferromagnetic metals suggests that a correction factor of ~2 is needed for\nthe spin polarization values obtained by lateral spin valve experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Exact solution for the dynamical decoupling of a qubit with telegraph\n  noise: We study the dissipative dynamics of a qubit that is afflicted by classical\nrandom telegraph noise and it is subject to dynamical decoupling. We derive\nexact formulas for the qubit dynamics at arbitrary working points in the limit\nof infinitely strong control pulses (bang-bang control) and we investigate in\ngreat detail the efficiency of the dynamical decoupling techniques both for\nGaussian and non-Gaussian (slow) noise at qubit pure dephasing and at optimal\npoint. We demonstrate that control sequences can be successfully implemented as\ndiagnostic tools to infer spectral proprieties of a few fluctuators interacting\nwith the qubit. The analysis is extended in order to include the effect of\nnoise in the pulses and we give upper bounds on the noise levels that can be\ntolerated in the pulses while still achieving efficient dynamical decoupling\nperformance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The transmission spectra of the graphene-based Fibonacci superlattice: We consider the gapped graphene superlattice (SL) constructed in accordance\nwith the Fibonacci rule. Quasi-periodic modulation is due to the difference in\nthe values of the energy gap in different SL elements. It is shown that the\neffective splitting of the allowed bands and thereby forming a series of gaps\nis realized under the normal incidence of electrons on the SL as well as under\noblique incidence. Energy spectra reveal periodical character on the whole\nenergy scale. The splitting of allowed bands is subjected to the inflation\nFibonacci rule. The gap associated with the new Dirac point is formed in every\nFibonacci generation. The location of this gap is robust against the change in\nthe SL period but at the same time it is sensitive to the ratio of barrier and\nwell widths; also it is weakly dependent on values of the mass term in the\nHamiltonian.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Chaos in two-dimensional Kepler problem with spin-orbit coupling: We consider classical two-dimensional Kepler system with spin-orbit coupling\nand show that at a sufficiently strong coupling it demonstrates a chaotic\nbehavior. The chaos emerges since the spin-orbit coupling reduces the number of\nthe integrals of motion as compared to the number of the degrees of freedom.\nThis reduction is manifested in the equations of motion as the emergence of the\nanomalous velocity determined by the spin orientation. By using analytical and\nnumerical arguments, we demonstrate that the chaotic behavior, being driven by\nthis anomalous term, is related to the system energy dependence on the initial\nspin orientation. We observe the critical dependence of the dynamics on the\ninitial conditions, where system can enter and exit a stability domain by very\nsmall changes in the initial spin orientation. Thus, this system can\ndemonstrate a reentrant order-from-disorder transition driven by very small\nvariations in the initial conditions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Entanglement spectrum and symmetries in non-Hermitian fermionic\n  non-interacting models: We study the properties of the entanglement spectrum in gapped\nnon-interacting non-Hermitian systems, and its relation to the topological\nproperties of the system Hamiltonian. Two different families of entanglement\nHamiltonians can be defined in non-Hermitian systems, depending on whether we\nconsider only right (or equivalently only left) eigenstates or a combination of\nboth left and right eigenstates. We show that their entanglement spectra can\nstill be computed efficiently, as in the Hermitian limit. We discuss how\nsymmetries of the Hamiltonian map into symmetries of the entanglement spectrum\ndepending on the choice of the many-body state. Through several examples in one\nand two dimensions, we show that the biorthogonal entanglement Hamiltonian\ndirectly inherits the topological properties of the Hamiltonian for line gapped\nphases, with characteristic singular and energy zero modes. The right (left)\ndensity matrix carries distinct information on the topological properties of\nthe many-body right (left) eigenstates themselves. In purely point gapped\nphases, when the energy bands are not separable, the relation between the\nentanglement Hamiltonian and the system Hamiltonian breaks down.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Conductance Fluctuations and Domain Depinning in Quasi-2D\n  Charge-Density-Wave 1T-TaS$_2$ Thin Films: We investigated the temperature dependence of the conductance fluctuations in\nthin films of the quasi-two-dimensional 1T-TaS$_2$ van der Waals material. The\nconductance fluctuations, determined from the derivative current-voltage\ncharacteristics of two-terminal 1T-TaS$_2$ devices, appear prominently at the\nelectric fields that correspond to the transitions between various\ncharge-density-wave macroscopic quantum condensate phases and at the onset of\nthe depinning of the charge density wave domains. The depinning threshold\nfield, $E_D$, monotonically increases with decreasing temperature within the\nnearly commensurate charge-density-wave phase. The $E_D$ value increases with\nthe decreasing 1T-TaS$_2$ film thickness, revealing the surface pinning of the\ncharge density waves. Our analysis suggests that depinning is absent in the\ncommensurate phase. It is induced by the electric field but facilitated by\nlocal heating. The measured trends for $E_D$ of the domain depinning are\nimportant for understanding the physics of charge density waves in\nquasi-two-dimensional crystals and for developing electronic devices based on\nthis type of quantum materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Formulation of Time-Resolved Counting Statistics Based on a\n  Positive-Operator-Valued Measure: We propose a derivation of the full counting statistics of electronic current\nbased on a positive-operator-valued measure. Our approach justifies the\nLevitov-Lesovik formula in the long-time limit, but can be generalized to the\ndetection of finite-frequency noise correlations. The combined action of the\nprojection postulate and the quantum formula for current noise at high\nfrequencies imply an additional white noise. Estimates for this additional\nnoise are in accordance with known experiments. We propose an experimental test\nof our conjecture by a simultaneous measurement of high- and low-frequency\nnoise.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Calculating interface transport parameters at finite temperatures:\n  Nonmagnetic interfaces: First-principles scattering calculations are used to investigate spin\ntransport through interfaces between diffusive nonmagnetic metals where the\nsymmetry lowering leads to an enhancement of the effect of spin-orbit coupling\n(SOC) and to a discontinuity of the spin currents passing through the\ninterfaces. From the conductance and local spin currents calculated for\nnonmagnetic bilayers, we extract values of the room temperature interface\nresistance $R_{\\rm I}$, of the spin memory loss parameter $\\delta$ and of the\ninterface spin Hall angle $\\Theta_{\\rm I}$ for nonmagnetic Au$|$Pt and Au$|$Pd\ninterfaces using a frozen thermal disorder scheme to model finite temperatures.\nSubstantial values of all three parameters are found with important\nconsequences for experiments involving nonmagnetic spacer and capping layers.\nThe temperature dependence of the interface parameters is determined for\nAu$|$Pt.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "2D transport and screening in topological insulator surface states: We study disorder effects on the surface states of the topological insulator\nBi$_2$Se$_3$ close to the topologically protected crossing point. Close to\ncharge neutrality, local fluctuations in carrier density arising from the\nrandom charged disorder in the environment result in electron and hole puddles\nthat dominate the electronic properties of these materials. By calculating the\npolarizability of the surface state using the random phase approximation, and\ndetermining the characteristics of puddles using the self-consistent\napproximation, we find that band asymmetry plays a crucial role in determining\nexperimentally measured quantities including the conductivity and the puddle\nautocorrelation length.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Floquet band structure of a semi-Dirac system: In this work we use Floquet-Bloch theory to study the influence of circularly\nand linearly polarized light on two-dimensional band structures with semi-Dirac\nband touching points, taking the anisotropic nearest neighbor hopping model on\nthe honeycomb lattice as an example. We find circularly polarized light opens a\ngap and induces a band inversion to create a finite Chern number in the\ntwo-band model. By contrast, linearly polarized light can either open up a gap\n(polarized in the quadratically dispersing direction) or split the semi-Dirac\nband touching point into two Dirac points (polarized in the linearly dispersing\ndirection) by an amount that depends on the amplitude of the light. Motivated\nby recent pump-probe experiments, we investigated the non-equilibrium spectral\nproperties and momentum-dependent spin-texture of our model in the Floquet\nstate following a quench in absence of phonons, and in the presence of phonon\ndissipation that leads to a steady-state independent of the pump protocol.\nFinally, we make connections to optical measurements by computing the frequency\ndependence of the longitudinal and transverse optical conductivity for this\ntwo-band model. We analyze the various contributions from inter-band\ntransitions and different Floquet modes. Our results suggest strategies for\noptically controlling band structures and experimentally measuring topological\nFloquet systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Intermediate phase and pseudo phase transition in an artificial spin ice\n  model: In this paper we conduct Monte Carlo simulations to investigate the\nthermodynamic properties of a geometry of artificial spin ice recently proposed\nin the literature that had been termed \"rewritable\" spin ice, for its\nexperimental realization allows total control over the microstates of the\nsystem. Our results show that in the thermodynamic limit a single phase\ntransition between a fully magnetized state and a paramagnetic state exists,\nwhereas for finite systems an intermediate phase also emerges, engendering a\nlow temperature pseudo phase transition. This intermediate phase is\ncharacterized by large magnetic domains separated by domain walls composed of\nmonopole-like excitations, resulting in low net magnetization values. We also\nshow that two types of low energy excitations that behave as magnetic monopoles\nemerge in the system, both of which are geometrically constrained to move along\na predefined path.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Majorana qubit decoherence by quasiparticle poisoning: We consider the problem of quasiparticle poisoning in a nanowire-based\nrealization of a Majorana qubit, where a spin-orbit-coupled semiconducting wire\nis placed on top of a (bulk) superconductor. By making use of recent\nexperimental data exhibiting evidence of a low-temperature residual\nnon-equilibrium quasiparticle population in superconductors, we show by means\nof analytical and numerical calculations that the dephasing time due to the\ntunneling of quasiparticles into the nanowire may be problematically short to\nallow for qubit manipulation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Diffusion and multifractality at the metal-insulator transition: We review the time evolution of wavepackets at the metal-insulator transition\nin two- and three-dimensional disordered systems. The importance of scale\ninvariance and multifractal eigenfunction fluctuations is stressed. The\nimplications of the frequency- and wavevector-dependence of the diffusion\ncoefficient are compared with the results of numerical simulations. We argue\nthat network models are particularly suited for the investigation of the\ndynamics of disordered systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-Markovian transients in transport across chiral quantum wires using\n  space-time non-equilibrium Green functions: We study a system of two non-interacting quantum wires with fermions of\nopposite chirality with a point contact junction at the origin across which\ntunneling can take place when an arbitrary time-dependent bias between the\nwires is applied. We obtain the exact dynamical non-equilibrium Green function\nby solving Dyson's equation analytically. Both the space-time dependent two and\nfour-point functions are written down in a closed form in terms of simple\nfunctions of position and time. This allows us to obtain, among other things,\nthe I-V characteristics for an arbitrary time-dependent bias. Our method is a\nsuperior alternative to competing approaches to non-equilibrium as we are able\nto account for transient phenomena as well as the steady state. We study the\napproach to steady state by computing the time evolution of the equal-time\none-particle Green function. Our method can be easily applied to the problem of\na double barrier contact whose internal properties can be adjusted to induce\nresonant tunneling leading to a conductance maximum. We then consider the case\nof a finite bandwidth in the point contact and calculate the non-equilibrium\ntransport properties which exhibit non-Markovian behaviour. When a subsequently\nconstant bias is suddenly switched on, the current shows a transient build up\nbefore approaching its steady state value in contrast to the infinite bandwidth\ncase. This transient property is consistent with numerical simulations of\nlattice systems using time-dependent DMRG (tDMRG) suggesting thereby that this\ntransient build up is merely due to the presence of a short distance cutoff in\nthe problem description and not on the other details.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Measuring electron energy distribution by current fluctuations: A recent concept of local noise sensor is extended to measure the energy\nresolved electronic energy distribution $f(\\varepsilon)$ at a given location\ninside a non-equilibrium normal metal interconnect. A quantitative analysis of\n$f(\\varepsilon)$ is complicated because of a nonlinear differential resistance\nof the noise sensor, represented by a diffusive InAs nanowire. Nevertheless, by\ncomparing the non-equilibrium results with reference equilibrium measurements,\nwe conclude that $f(\\varepsilon)$ is indistinguishable from the Fermi\ndistribution.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous thermoelectric properties of a Floquet topological insulator\n  with spin momentum non-orthogonality: The spin momentum non-orthogonality in 3D topological insulators leads to\nmodification of the spin texture and brings in an out-of-plane spin\npolarization component. Apart from spin texture, the anomalous thermoelectric\nproperties of these materials are worth studying. In this paper, we have\npointed out that the off resonant light used to irradiate the surface states,\ninduces a gap, which becomes momentum dependent due to the presence of\nnon-orthogonal terms in the Hamiltonian. Importantly, to maintain the off\nresonant condition of light, the momentum value should satisfy a bound.\nFurthermore, the momentum dependent gap causes a topological transition at\nhigher value of momentum, which is important to analyse the unusual double peak\nstructure of the Nernst and electrical conductivities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nano-beam clamping revisited: Within recent years, the field of nano-mechanics has diversified in a variety\nof applications, ranging from quantum information processing to biological\nmolecules recognition. Among the diversity of devices produced these days, the\nsimplest (but versatile) element remains the doubly-clamped beam: it can store\nvery large tensile stresses (producing high resonance frequencies $f_0$ and\nquality factors $Q$), is interfaceable with electric setups (by means of\nconductive layers), and can be produced easily in clean rooms (with scalable\ndesigns including multiplexing). Besides, its mechanical properties are the\nsimplest to describe. Resonance frequencies and $Q$s are being modeled, with as\nspecific achievement the ultra-high quality resonances based on ``soft\nclamping'' and ``phonon shields''. Here, we demonstrate that the fabrication\nundercut of the clamping regions of basic nano-beams produces a ``natural soft\nclamping'', given for free. We present the analytic theory that enables to fit\nexperimental data, which can be used for $\\{ Q , f_0 \\}$ design: beyond Finite\nElement Modeling validation, the presented expressions provide a profound\nunderstanding of the phenomenon, with both a Q enhancement and a downwards\nfrequency shift.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spectral statistics of disordered metals in the presence of several\n  Aharonov-Bohm fluxes: The form factor for spectral correlations in a diffusive metal is calculated\nin the presence of several Aharonov-Bohm fluxes. When the fluxes $\\phi$ are\nequal, the correlations are universal functions of $n g^2 \\phi$ where $g$ is\nthe dimensionless conductance and $n$ is the number of applied fluxes. This\nexplains recent flux dependence of the correlations found numerically at the\nmetal-insulator transition.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetopumping current in graphene Corbino pump: We study conductance and adiabatic pumped charge and spin currents in a\ngraphene quantum pump with Corbino geometry in the presence of an applied\nperpendicular magnetic field. The pump is driven by the periodic and out of\nphase modulations of the magnetic field and an electrostatic potential applied\nto the ring area of the pump. We show that the Zeeman splitting, despite of its\nsmallness, can suppress the conductance oscillations at the zero doping and in\na threshold value for the flux piercing the ring area which depends on the\ninner lead radius and thus on the flux penetrating in it. Moreover, it\ngenerates a considerable spin conductance at infinitesimal nonzero doping and\nat the magnetic flux, that charge conductance starts to suppress. We find that\nthe pumped charge and spin currents increase by the magnetic field with small\noscillations until they start to suppress due to the effect of the nonzero\ndoping and the Zeeman splitting. In graphene Corbino pumps with small inner\nleads the Zeeman splitting shows its effect in a large value of the magnetic\nfield and thus we can get a considerable pumped charge and spin currents at the\nenough small magnetic fields.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Microscopic analysis of shot-noise suppression in nondegenerate\n  diffusive conductors: We present a theoretical investigation of shot-noise suppression due to\nlong-range Coulomb interaction in nondegenerate diffusive conductors.\nCalculations make use of an ensemble Monte Carlo simulator self-consistently\ncoupled with a one-dimensional Poisson solver. We analyze the noise in a\nlightly doped active region surrounded by two contacts acting as thermal\nreservoirs. By taking the doping of the injecting contacts and the applied\nvoltage as variable parameters, the influence of elastic and inelastic\nscattering in the active region is investigated. The transition from ballistic\nto diffusive transport regimes under different contact injecting statistics is\nanalyzed and discussed. Provided significant space-charge effects take place\ninside the active region, long-range Coulomb interaction is found to play an\nessential role in suppressing the shot noise at $qU \\gg k_BT$. In the elastic\ndiffusive regime, momentum space dimensionality is found to modify the\nsuppression factor $\\gamma$, which within numerical uncertainty takes values\nrespectively of about 1/3, 1/2 and 0.7 in the 3D, 2D and 1D cases. In the\ninelastic diffusive regime, shot noise is suppressed to the thermal value.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Prediction of inelastic light scattering spectra from electronic\n  collective excitations in GaAs/AlGaAs core-multishell nanowires: We predict inelastic light scattering spectra from electron collective\nexcitations in a coaxial quantum well embedded in a core-multishell GaAs/AlGaAs\nnanowire. The complex composition, the hexagonal cross section and the remote\ndoping of typical samples are explicitly included, and the free electron gas is\nobtained by a DFT approach. Inelastic light scattering cross sections due to\ncharge and spin collective excitations belonging to quasi-1D and quasi-2D\nstates, which coexist in such radial heterostructures, are predicted in the\nnon-resonant approximation from a fully three-dimensional multi-subband TDDFT\nformalism. We show that collective excitations can be classified in azimuthal,\nradial and longitudinal excitations, according to the associated density\nfluctuations, and we suggest that their character can be exposed by specific\nspectral dispersion of inelastic light scattering along different planes of the\nheterostructure.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "55Mn NMR in Mn12 acetate: Hyperfine interaction and magnetic relaxation\n  of cluster: The 55Mn NMR in oriented powder Mn12Ac has been investigated at 1.4-2.0 K in\nzero field and with external fields along the c-axis. Three kinds of 55Mn NMR\ncomposed of five-fold quadrupole-split lines for I=5/2 nuclei have been\ninterpreted to arise from Mn4+ ion, and two crystallographically-inequivalent\nMn3+ ions, respectively. It is found that the isotropic hyperfine field in the\nMn4+ ion with 3d3 configuration indicates a large amount of reduction (26%) as\ncompared with the theoretical evaluation. In the analysis for the hyperfine\nfield of Mn3+ ions with 3d4 configuration, we have taken into account of the\nanisotropic dipolar contribution in addition to the Fermi-contact term in order\nto explain two kinds of 55Mn NMR frequencies in Mn3+ ions in inequivalent\nsites. By using the hyperfine coupling constants of twelve manganese ions in\nMn12Ac, the total hyperfine interaction of the ferrimagnetic ground state of\nS=10 has been determined to amount to 0.3 cm-1 in magnitude at most, the\nmagnitude of which corresponds to the nuclear hyperfine field he(0.32 kG seen\nby Mn12 cluster spin. The relaxation of the cluster magnetization was\ninvestigated by observing the recovery of the 55Mn spin-echo intensity in the\nfields of 0.20-1.90 T along the c-axis at 2.0 K. It was found that the\nmagnetization of the cluster exhibits the (t-recovery in the short time regime.\nThe relaxation time decreases with increasing external field following\nsignificant dips at every 0.45 T. This is interpreted to be due to the effects\nof thermally-assisted quantum tunneling between the spin states at magnetic\nlevel crossings.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological superconductivity in lead nanowires: Superconductors with an odd number of bands crossing the Fermi energy have\ntopologically protected Andreev states at interfaces, including Majorana states\nin one dimensional geometries. Superconductivity, a low number of 1D channels,\nlarge spin orbit coupling, and a sizeable Zeeman energy, are present in lead\nnanowires produced by nanoindentation of a Pb tip on a Pb substrate, in\nmagnetic fields higher than the Pb bulk critical field. A number of such\ndevices have been analyzed. In some of them, the dependence of the critical\ncurrent on magnetic field, and the Multiple Andreev Reflections observed at\nfinite voltages, are compatible with the existence of topological\nsuperconductivity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunneling through two resonant levels: fixed points and conductances: We study point contact tunneling between two leads of a Tomonaga-Luttinger\nliquid through two degenerate resonant levels in parallel. This is one of the\nsimplest cases of a quantum junction problem where the Fermi statistics of the\nelectrons plays a non-trivial role through the Klein factors appearing in\nbosonization. Using a mapping to a `generalized Coulomb model' studied in the\ncontext of the dissipative Hofstadter model, we find that any asymmetry in the\ntunneling amplitudes from the two leads grows at low temperatures, so that\nultimately there is no conductance across the system. For the symmetric case,\nwe identify a non-trivial fixed point of this model; the conductance at that\npoint is generally different from the conductance through a single resonant\nlevel.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermal fluctuation field for current-induced domain wall motion: Current-induced domain wall motion in magnetic nanowires is affected by\nthermal fluctuation. In order to account for this effect, the\nLandau-Lifshitz-Gilbert equation includes a thermal fluctuation field and\nliterature often utilizes the fluctuation-dissipation theorem to characterize\nstatistical properties of the thermal fluctuation field. However, the theorem\nis not applicable to the system under finite current since it is not in\nequilibrium. To examine the effect of finite current on the thermal\nfluctuation, we adopt the influence functional formalism developed by Feynman\nand Vernon, which is known to be a useful tool to analyze effects of\ndissipation and thermal fluctuation. For this purpose, we construct a quantum\nmechanical effective Hamiltonian describing current-induced domain wall motion\nby generalizing the Caldeira-Leggett description of quantum dissipation. We\nfind that even for the current-induced domain wall motion, the statistical\nproperties of the thermal noise is still described by the\nfluctuation-dissipation theorem if the current density is sufficiently lower\nthan the intrinsic critical current density and thus the domain wall tilting\nangle is sufficiently lower than pi/4. The relation between our result and a\nrecent result, which also addresses the thermal fluctuation, is discussed. We\nalso find interesting physical meanings of the Gilbert damping alpha and the\nnonadiabaticy parameter beta; while alpha characterizes the coupling strength\nbetween the magnetization dynamics (the domain wall motion in this paper) and\nthe thermal reservoir (or environment), beta characterizes the coupling\nstrength between the spin current and the thermal reservoir.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A scalar photon theory for near-field radiative heat transfer: We study a one-dimensional model of radiative heat transfer for which the\neffect of the electromag- netic field is only from the scalar potential and\nthereby ignoring the vector potential contribution. This is a valid assumption\nwhen the distances between objects are of the order of nanometers. Using Lorenz\ngauge, the scalar field is quantized with the canonical quantization scheme,\ngiving rise to scalar photons. In the limit as the speed of light approaches\ninfinity, the theory reduces to a pure Coulomb interaction governed by the\nPoisson equation. The model describes very well parallel plate capacitor\nphysics, where a new length scale related to its capacitance emerges. Shorter\nthan this length scale we see greater radiative heat transfer. This differs\nmarkedly from the usual Rytov fluctuational electrodynamics theory in which the\nenhancement is due to evanescent modes shorter than the thermal wavelengths.\nOur theory may explain recent experiments where charge fluctuations instead of\ncurrent fluctuations play a dominant role in radiative heat transfer. Finally,\ndue to the asymmetric electron-bath couplings, thermal rectification effects\nare also observed and reported.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum non-demolition measurements of a qubit coupled to a harmonic\n  oscillator: We theoretically describe the weak measurement of a two-level system (qubit)\nand quantify the degree to which such a qubit measurement has a quantum\nnon-demolition (QND) character. The qubit is coupled to a harmonic oscillator\nwhich undergoes a projective measurement. Information on the qubit state is\nextracted from the oscillator measurement outcomes, and the QND character of\nthe measurement is inferred by the result of subsequent measurements of the\noscillator. We use the positive operator valued measure (POVM) formalism to\ndescribe the qubit measurement. Two mechanisms lead to deviations from a\nperfect QND measurement: (i) the quantum fluctuations of the oscillator, and\n(ii) quantum tunneling between the qubit states $|0>$ and $|1>$ during\nmeasurements. Our theory can be applied to QND measurements performed on\nsuperconducting qubits coupled to a circuit oscillator.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Extended Hubbard model for mesoscopic transport in donor arrays in\n  silicon: Arrays of dopants in silicon are promising platforms for the quantum\nsimulation of the Fermi-Hubbard model. We show that the simplest model with\nonly on-site interaction is insufficient to describe the physics of an array of\nphosphorous donors in silicon due to the strong intersite interaction in the\nsystem. We also study the resonant tunneling transport in the array at low\ntemperature as a mean of probing the features of the Hubbard physics, such as\nthe Hubbard bands and the Mott gap. Two mechanisms of localization which\nsuppresses transport in the array are investigated: The first arises from the\nelectron-ion core attraction and is significant at low filling; the second is\ndue to the sharp oscillation in the tunnel coupling caused by the intervalley\ninterference of the donor electron's wavefunction. This disorder in the tunnel\ncoupling leads to a steep exponential decay of conductance with channel length\nin one-dimensional arrays, but its effect is less prominent in two-dimensional\nones. Hence, it is possible to observe resonant tunneling transport in a\nrelatively large array in two dimensions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nonreciprocal Emergence of Hybridized Magnons in magnetic thin Films: We investigate the transfer and control of nonreciprocity through magnons\nthemselves in permalloy thin films deposited on surface oxide silicon\nsubstrate. Evidences of nonreciprocal emergence of hybridized dipole exchange\nmagnons (spin waves) at two permalloy surfaces are provided by studying magnon\ntransmission and asymmetry, via Brillouin light scattering measurements. The\ndipole dominated spin wave and exchange dominated spin wave are found to be\nlocalized near the top and bottom surfaces, respectively, and traveling along\nopposite directions. The nonreciprocity and the localization are intertwined\nand ca n be tuned by an in plane magnetic field. The effects are well explained\nby the magnetostatic theory and can be quantitatively reproduced by the\nmicromagnetic simulations. Our findings provide a simple and flexible approach\nto nonreciprocal all magnon logi c devices with highly compatible with silicon\nbased integrated circuit technology.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spaser Spectroscopy with Subwavelength Spatial Resolution: A new method for high-sensitivity subwavelength spectromicroscopy is proposed\nbased on the usage of a spaser (near-field laser) in the form of a scanning\nprobe microscope tip. The high spatial resolution is defined by the tip's\ncurvature, as is the case for apertureless scanning near-field optical\nmicroscopy. In contrast to the latter method, we suggest using radiationless\nplasmon pumping by neighbouring quantum dots instead of irradiation of the tip\nby an external laser beam. The spaser generation spectrum is analyzed. The\nplasmon generation is suppressed due to absorption at the transition\nfrequencies of the neighbouring nano-objects (molecules or clusters) under\nstudy. As a result, narrow dips appear in the wide plasmon generation spectrum.\nFurther, the highest sensitivity is achieved near the spaser generation\nthreshold. The sensitivity of the spaser spectromicroscope is estimated.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Controlled Growth of a Line Defect in Graphene and Implications for\n  Gate-Tunable Valley Filtering: Atomically precise tailoring of graphene can enable unusual transport\npathways and new nanometer-scale functional devices. Here we describe a recipe\nfor the controlled production of highly regular \"5-5-8\" line defects in\ngraphene by means of simultaneous electron irradiation and Joule heating by\napplied electric current. High-resolution transmission electron microscopy\nreveals individual steps of the growth process. Extending earlier theoretical\nwork suggesting valley-discriminating capabilities of a graphene 5-5-8 line\ndefect, we perform first-principles calculations of transport and find a strong\nenergy dependence of valley polarization of the charge carriers across the\ndefect. These findings inspire us to propose a compact electrostatically gated\n\"valley valve\" device, a critical component for valleytronics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological phase transitions in the non-Abelian honeycomb lattice: Ultracold Fermi gases trapped in honeycomb optical lattices provide an\nintriguing scenario, where relativistic quantum electrodynamics can be tested.\nHere, we generalize this system to non-Abelian quantum electrodynamics, where\nmassless Dirac fermions interact with effective non-Abelian gauge fields. We\nshow how in this setup a variety of topological phase transitions occur, which\narise due to massless fermion pair production events, as well as pair\nannihilation events of two kinds: spontaneous and strongly-interacting induced.\nMoreover, such phase transitions can be controlled and characterized in optical\nlattice experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Carbon Nanotubes as Nanoelectromechanical Systems: We theoretically study the interplay between electrical and mechanical\nproperties of suspended, doubly clamped carbon nanotubes in which charging\neffects dominate. In this geometry, the capacitance between the nanotube and\nthe gate(s) depends on the distance between them. This dependence modifies the\nusual Coulomb models and we show that it needs to be incorporated to capture\nthe physics of the problem correctly. We find that the tube position changes in\ndiscrete steps every time an electron tunnels onto it. Edges of Coulomb\ndiamonds acquire a (small) curvature. We also show that bistability in the tube\nposition occurs and that tunneling of an electron onto the tube drastically\nmodifies the quantized eigenmodes of the tube. Experimental verification of\nthese predictions is possible in suspended tubes of sub-micron length.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Macroscopic resonant tunneling of magnetic flux: We have developed a quantitative theory of resonant tunneling of magnetic\nflux between discrete macroscopically distinct quantum states in SQUID systems.\nThe theory is based on the standard density-matrix approach. Its new elements\ninclude the discussion of the two different relaxation mechanisms that exist\nfor the double-well potential, and description of the ``photon-assisted''\ntunneling driven by external rf radiation. It is shown that in the case of\ncoherent flux dynamics, rf radiation should lead to splitting of the peaks of\nresonant flux tunneling, indicating that the resonant tunneling is a convenient\ntool for studying macroscopic quantum coherence of flux.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Polariton transport in one-dimensional channels: We study theoretically the transport of linearly polarized exciton-polaritons\nin a quasi one-dimensional microcavity channel separating two polariton\ncondensates generated by optical pumping. The direction and value of mass and\nspin currents are controlled by the relative phase and polarisation of two\ncondensates, as in the stationary Josephson effect. However, due to dissipation\nand particle-particle interactions, the current denisty is inhomogeneous: it\nstrongly depends on the coordinate along the axis of the channel. A stationary\nspin domain can be created in the channel, its position would be sensitive to\nthe phase difference between two bordering condensates.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Graphene plasmons and retardation: strong light-matter coupling: We study the retardation regime of doped graphene plasmons, given by the\nnominal crossing of the unretarded plasmon and light-cone. In addition to\nmodifications in the plasmon dispersion relation, retardation implies strong\ncoupling between propagating light and matter, even for homogeneous graphene,\nwhich opens up the possibility of efficient plasmonics in simple graphene\ndevices. We exemplify this enhancement in a double-layer configuration that\nexhibits {\\em perfect} (if lossless) light transmissions across a classically\nforbidden region, providing a simpler analog of the corresponding phenomenon in\nperforated metal sheets. We also show that (broad) Fabry-P\\'erot resonances\npresent without graphene turn into sharply peaked, quasi-discrete modes in the\npresence of graphene where graphene's response function is given by the typical\nFano lineshape.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Landau levels, self-adjoint extensions and Hall conductivity on a cone: In this work we obtain the Landau levels and the Hall conductivity at zero\ntemperature of a two-dimensional electron gas on a conical surface. We\ninvestigate the integer quantum Hall effect considering two different\napproaches. The first one is an extrinsic approach which employs an effective\nscalar potential that contains both the Gaussian and the mean curvature of the\nsurface. The second one, an intrinsic approach where the Gaussian curvature is\nthe sole term in the scalar curvature potential. From a theoretical point of\nview, the singular Gaussian curvature of the cone may affect the wave functions\nand the respective Landau levels. Since this problem requests {\\it self-adjoint\nextensions}, we investigate how the conical tip could influence the integer\nquantum Hall effect, comparing with the case were the coupling between the wave\nfunctions and the conical tip is ignored. This last case corresponds to the\nso-called {\\it Friedrichs extension}. In all cases, the Hall conductivity is\nenhanced by the conical geometry depending on the opening angle. There are a\nconsiderable number of theoretical papers concerned with the self-adjoint\nextensions on a cone and now we hope the work addressed here inspires\nexperimental investigation on these questions about quantum dynamics on a cone.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Engineering Quantum Anomalous Hall Plateaus and Anti-Chiral States with\n  AC Fields: We investigate the AC electric field induced quantum anomalous Hall effect in\nhoneycomb lattices and derive the full phase diagram for arbitrary field\namplitude and phase polarization. We show how to induce anti-chiral edge modes\nas well as topological phases characterized by a Chern number larger than $1$\nby means of suitable drivings. In particular, we find that the Chern number\ndevelops plateaus as a function of the frequency, providing an time-dependent\nanalogue to the ones in the quantum Hall effect.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Walker-like Domain Wall breakdown in layered Antiferromagnets driven by\n  staggered spin-orbit fields: Within linear continuum theory, no magnetic texture can propagate faster than\nthe maximum group velocity of its spin waves. Here we report a transient regime\ndue to the appearance of additional antiferromagnetic textures that breaks the\nLorentz translational invariance of the magnetic system by atomistic spin\ndynamics simulations. This dynamical regime is akin to domain wall\nWalker-breakdown in ferromagnets and involves the nucleation of an\nantiferromagnetic domain wall pair. Subsequently, one of the nucleated\n180$^{\\circ}$ domain wall creates with the original domain wall a 360$^{\\circ}$\nspin-rotation which remains static even under the action of the spin-orbit\nfield. The other 180$^{\\circ}$ domain wall becomes accelerated to\nsuper-magnonic speeds. Under large spin-orbit fields, multiple domain wall\ngeneration and recombination is obtained which may explain the recently\nexperimentally observed current pulse induce shattering of large domain\nstructures into small fragmented domains and the subsequent slow recreation of\nlarge-scale domain formation prior current pulse.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamical Shiba states by precessing magnetic moments in an s-wave\n  superconductor: We study theoretically the dynamics of a Shiba state forming around\nprecessing classical spin in an s-wave superconductor. Utilizing a rotating\nwave description for the precessing magnetic impurity, we find the resulting\nShiba bound state quasi-energy and the spatial extension of the Shiba\nwavefunction. We show that such a precession pertains to dc charge and spin\ncurrents flowing through a normal STM tip tunnel coupled to the superconductor\nin the vicinity of the impurity. We calculate these currents and find that they\nstrongly depend on the magnetic impurity precession frequency, precession\nangle, and on the position of the Shiba energy level in the superconducting\ngap. The resulting charge current is found to be proportional to the difference\nbetween the electron and hole wavefunctions of the Shiba state, being a direct\nmeasure for such an asymmetry. By dynamically driving the impurity one can\ninfer the spin dependence of the Shiba states in the absence of a\nspin-polarized STM tip",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nonlinear coherent transport of waves in disordered media: We present a diagrammatic theory for coherent backscattering from disordered\ndilute media in the nonlinear regime. The approach is non-perturbative in the\nstrength of the nonlinearity. We show that the coherent backscattering\nenhancement factor is strongly affected by the nonlinearity, and corroborate\nthese results by numerical simulations. Our theory can be applied to several\nphysical scenarios like scattering of light in nonlinear Kerr media, or\npropagation of matter waves in disordered potentials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Impurity-directed Transport within a Finite Disordered Lattice: We consider a finite, disordered 1D quantum lattice with a side-attached\nimpurity. We study theoretically the transport of a single electron from the\nimpurity into the lattice, at zero temperature. The transport is dominated by\nAnderson localization and, in general, the electron motion has a random\ncharacter due to the lattice disorder. However, we show that by adjusting the\nimpurity energy the electron can attain quasi-periodic motions, oscillating\nbetween the impurity and a small region of the lattice. This region corresponds\nto the center of a localized state in the lattice with an energy matched by\nthat of the impurity. By precisely tuning the impurity energy, the electron can\nbe set to oscillate between the impurity and a region far from the impurity,\neven distances larger than the Anderson localization length. The electron\noscillations result from the interference of hybridized states, which have some\nresemblance to Pendry's necklace states [J. B. Pendry, J. Phys. C: Solid State\nPhys. 20, 733-742 (1987)]. The dependence of the electron motion on the\nimpurity energy gives a potential mechanism for selectively routing an electron\ntowards different regions of a 1D disordered lattice.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spacer-layer-tunable magnetism and high-field topological Hall effect in\n  topological insulator heterostructures: Controlling magnetic order in magnetic topological insulators (MTIs) is a key\nto developing spintronic applications with MTIs, and is commonly achieved by\nchanging the magnetic doping concentration, which inevitably affects\nspin-orbit-coupling strength and the very topological properties. Here, we\ndemonstrate tunable magnetic properties in topological heterostructures over a\nwide range, from a ferromagnetic phase with Curie temperature of around 100 K\nall the way to a paramagnetic phase, while keeping the overall chemical\ncomposition the same, by controlling the thickness of non-magnetic spacer\nlayers between two atomically-thin magnetic layers. This work showcases that\nspacer-layer control is a powerful tool to manipulate magneto-topological\nfunctionalities in MTI heterostructures. Furthermore, the interaction between\nthe MTI and the Cr2O3 buffer layers also led to robust topological Hall effect\nsurviving up to a record-high 6 T of magnetic field, shedding light on the\ncritical role of interfacial layers in thin film topological materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous Finite Size Effects on Surface States in the Topological\n  Insulator Bi$_2$Se$_3$: We study how the surface states in the strong topological insulator\nBi$_2$Se$_3$ are influenced by finite size effects, and compare our results\nwith those recently obtained for 2D topological insulator HgTe. We demonstrate\ntwo important distinctions: \\textit{(i)} contrary to HgTe, the surface-states\nin Bi$_2$Se$_3$ display a remarkable robustness towards decreasing the width\n$L$ down to a few nm, thus ensuring that the topological surface states remain\nintact, and \\textit{(ii)} the gapping due to the hybridization of the surface\nstates features an oscillating exponential decay as a function of $L$ in\nBi$_2$Se$_3$ in sharp contrast to HgTe. Our findings suggest that Bi$_2$Se$_3$\nis suitable for nanoscale applications in quantum computing or spintronics.\nAlso, we propose a way to experimentally detect both of the predicted effects.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Phonon Driven Nonlinear Electrical Behavior in Molecular Devices: Electronic transport in a model molecular device coupled to local phonon\nmodes is theoretically analyzed. The method allows for obtaining an accurate\napproximation of the system's quantum state irrespective of the electron and\nphonon energy scales. Nonlinear electrical features emerge from the calculated\ncurrent-voltage characteristics. The quantum corrections with respect to the\nadiabatic limit characterize the transport scenario, and the polaronic\nreduction of the effective device-lead coupling plays a fundamental role in the\nunusual electrical features.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "High-Chern number phase in the topological insulator multilayer\n  structures: The high-Chern number phases with a Chern number C>1 have been observed in a\nrecent experiment that performed on the topological insulator (TI) multilayer\nstructures, consisting of the alternating magnetic-doped and undoped TI layers.\nIn this paper, we develop an effective method to determine the Chern numbers in\nthe TI multilayer structures and then make a systematic study on the Chern\nnumber phase diagrams that are modulated by the magnetic doping and the middle\nlayer thickness. We point out that in the multilayer structure, the high-C\nbehavior can be attributed to the band inversion mechanisms. Moreover, we find\nthat the lowest bands may be multifold degenerate around the Gamma point, and\nwhen they are inverted, the Chern number change will be larger than one.\nBesides the TI multilayer structures implemented in the experiment, we also\nexplore the high-C phase realizations in two other kinds of the TI multilayer\nstructures. The implications of our results for experiments are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Correlated breakdown of carbon nanotubes in an ultra-high density\n  aligned array: We demonstrate that in a densely packed aligned array of single walled carbon\nnanotubes, the breakdown of one nanotube leads to a highly correlated breakdown\nof neighboring nanotubes, thereby producing a nano-fissure. We show that the\norigin of the correlation is the electrostatic field of the broken nanotubes\nthat produces locally inhomogeneous current and Joule heating distributions in\nthe neighboring intact nanotubes triggering their breakdowns in the vicinity of\nthe broken nanotubes. Our results suggest that the densely aligned array\nbehaves like a correlated solid.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum anomalous Hall effect in atomic crystal layers from in-plane\n  magnetization: We theoretically report that, with \\textit{in-plane} magnetization, the\nquantum anomalous Hall effect (QAHE) can be realized in two-dimensional atomic\ncrystal layers with preserved inversion symmetry but broken out-of-plane mirror\nreflection symmetry. We take the honeycomb lattice as an example, where we find\nthat the low-buckled structure, which makes the system satisfy the symmetric\ncriteria, is crucial to induce QAHE. The topologically nontrivial bulk gap\ncarrying a Chern number of $\\mathcal{C}=\\pm1$ opens in the vicinity of the\nsaddle points $M$, where the band dispersion exhibits strong anisotropy. We\nfurther show that the QAHE with electrically tunable Chern number can be\nachieved in Bernal-stacked multilayer systems, and the applied interlayer\npotential differences can dramatically decrease the critical magnetization to\nmake the QAHE experimentally feasible.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Time-Delay Polaritonics: Non-linearity and finite signal propagation speeds are omnipresent in nature,\ntechnologies, and real-world problems, where efficient ways of describing and\npredicting the effects of these elements are in high demand. Advances in\nengineering condensed matter systems, such as lattices of trapped condensates,\nhave enabled studies on non-linear effects in many-body systems where exchange\nof particles between lattice nodes is effectively instantaneous. Here, we\ndemonstrate a regime of macroscopic matter-wave systems, in which ballistically\nexpanding condensates of microcavity exciton-polaritons act as picosecond,\nmicroscale non-linear oscillators subject to time-delayed interaction. The ease\nof optical control and readout of polariton condensates enables us to explore\nthe phase space of two interacting condensates up to macroscopic distances\nhighlighting its potential in extended configurations. We demonstrate\ndeterministic tuning of the coupled-condensate system between fixed point and\nlimit cycle regimes, which is fully reproduced by time-delayed coupled\nequations of motion similar to the Lang-Kobayashi equation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Phase transitions on the surface of a carbon nanotube: A suspended carbon nanotube can act as a nanoscale resonator with remarkable\nelectromechanical properties and the ability to detect adsorption on its\nsurface at the level of single atoms. Understanding adsorption on nanotubes and\nother graphitic materials is key to many sensing and storage applications. Here\nwe show that nanotube resonators offer a powerful new means of investigating\nfundamental aspects of adsorption on carbon, including the collective behaviour\nof adsorbed matter and its coupling to the substrate electrons. By monitoring\nthe vibrational resonance frequency in the presence of noble gases, we observe\nthe formation of monolayers on the cylindrical surface and phase transitions\nwithin these monolayers, and simultaneous modification of the electrical\nconductance. The monolayer observations also demonstrate the possibility of\nstudying the fundamental behaviour of matter in cylindrical geometry.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A spin dynamics approach to solitonics: It is spatial dispersion which is exclusively responsible for the emergence\nof exchange interaction and magnetic ordering. In contrast, magneto-crystalline\nanisotropy present in any realistic material brings in a certain non-linearity\nto the equation of motion. Unlike homogeneous ferromagnetic ordering a variety\nof non-collinear ground state configurations emerge as a result of competition\namong exchange, anisotropy, and dipole-dipole interaction. These particle-like\nstates, e.g. magnetic soliton, skyrmion, domain wall, form a spatially\nlocalised clot of magnetic energy. In this paper we explore topologically\nprotected magnetic solitons that might potentially be applied for logical\noperations and/or information storage in the rapidly advancing filed of\nsolitonics (and skyrmionics). An ability to easily create, address, and\nmanipulate such structures is among the prerequisite forming a basis of -onics\ntechnology, and is investigated in detail here using numerical and analytical\ntools.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic Bloch oscillation in bilayer graphene gradient superlattices: We investigate the electronic Bloch oscillation in bilayer graphene gradient\nsuperlattices using transfer matrix method. By introducing two kinds of\ngradient potentials of square barriers along electrons propagation direction,\nwe find that Bloch oscillations up to terahertz can occur. Wannier-Stark\nladders, as the counterpart of Bloch oscillation, are obtained as a series of\nequidistant transmission peaks, and the localization of the electronic wave\nfunction is also signature of Bloch oscillation. Forthermore, the period of\nBloch oscillation decreases linearly with increasing gradient of barrier\npotentials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Microscopic Theory of Skyrmions in Quantum Hall Ferromagnets: We present a microscopic theory of skyrmions in the monolayer quantum Hall\nferromagnet. It is a peculiar feature of the system that the number density and\nthe spin density are entangled intrinsically as dictated by the W$%_{\\infty}$\nalgebra. The skyrmion and antiskyrmion states are constructed as W$_{\\infty\n}$-rotated states of the hole-excited and electron-excited states,\nrespectively. They are spin textures accompanied with density modulation that\ndecreases the Coulomb energy. We calculate their excitation energy as a\nfunction of the Zeeman gap and compared the result with experimental data.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamics and condensation of polaritons in an optical nanocavity coupled\n  to two-dimensional materials: We present a comprehensive investigation of the light-matter interaction\ndynamics in two-dimensional materials coupled with a spectrally isolated cavity\nmode in the strong coupling regime. The interaction between light and matter\nbreaks the translational symmetry of excitons in the two-dimensional lattice\nand results in the emergence of a localized polariton state. Employing a novel\napproach involving transformation to exciton reaction coordinates, we derive a\nMarkovian master equation to describe the formation of a macroscopic population\nin the localized polariton state. Our study shows that the construction of a\nlarge-scale polariton population is affected by correction terms addressing the\nbreakdown of translational symmetry. Increasing the spatial width of the cavity\nmode increases the Coulomb scattering rates while the correction terms saturate\nand affect the system's dynamics progressively less. Tuning the lattice\ntemperature can induce bistability and hysteresis with different origins than\nthose recognized for quantum wells in larger microcavities. We identify a limit\ntemperature $T_{\\mathrm{l}}$ as a key factor for stimulated emissions and\nforming a macroscopic population, enriching our understanding of strong\ncoupling dynamics in systems with extreme confinement.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hole-doping-induced half-metallic ferromagnetism in highly-air-stable\n  PdSe2 monolayer under uniaxial stress: Two-dimensional (2D) high-temperature ferromagnetic materials are important\nfor spintronic application. Fortunately, a highly-air-stable PdSe$_2$ monolayer\nsemiconductor has been made through exfoliation from the layered bulk material.\nIt is very highly desirable to realize robust ferromagnetism, even\nhalf-metallic ferromagnetism (100\\% spin polarization), in such excellent\nnonmagnetic monolayer semiconductors. Here, the first-principles investigation\nshows that the PdSe$_2$ monolayer can be made to attain Stoner ferromagnetism\nwith the maximal Curie temperature reaching to 800K, and the hole concentration\nthreshold for ferromagnetism decreases with applied uniaxial stress.\nFurthermore, half-metallicity can be achieved in some hole concentration\nregions. For the strain of 10\\% (uniaxial tensile stress of 4.4 N/m), the\nmonolayer can attain half-metallic ferromagnetism up to 150 K. The magnetic\nanisotropic energy is suitable to not only stabilizing the 2D ferromagnetism\nbut also realizing fast magnetization reversal. The magnetization can be also\ncontrolled by applying a transverse uniaxial stress. The highly-air-stable\nPdSe$_2$ monolayer, with these advantages, should be promising for spintronic\napplications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Selective Conduction of Organic Molecules via Free-Standing Graphene: A race is held between ten species of organic gas molecules on a graphene\nsubstrate driven by thermal gradients via molecular dynamics. Fast conduction\nof the molecules is observed with selectivity for aromatic compounds. This\nselectivity stems from the fact that the planar structure of the aromatic\nmolecule helps keep a shorter distance to the substrate, which is the key to\nthe driving force at the gas-solid interface. The drift velocity monotonically\nincreases with decreasing molecule density, with no ballistic transport\nobservable even for a single molecule. A non-linear regime is discovered for\nthe conduction of benzene molecules under large thermal gradients. At low\ntemperature, molecules formed aggregation and move collectively along specific\npath in the graphene substrate.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunable Sample-wide Electronic Kagome Lattice in Low-angle Twisted\n  Bilayer Graphene: Overlaying two graphene layers with a small twist angle can create a moire\nsuperlattice to realize exotic phenomena that are entirely absent in graphene\nmonolayer. A representative example is the predicted formation of localized\npseudo-Landau levels (PLLs) with Kagome lattice in tiny-angle twisted bilayer\ngraphene (TBG) with theta < 0.3 deg when the graphene layers are subjected to\ndifferent electrostatic potentials. However, this was shown only for the model\nof rigidly rotated TBG which is not realized in reality due to an interfacial\nstructural reconstruction. It is believed that the interfacial structural\nreconstruction strongly inhibits the formation of the PLLs. Here, we\nsystematically study electronic properties of the TBG with 0.075 deg < theta <\n1.2 deg and demonstrate, unexpectedly, that the PLLs are quite robust for all\nthe studied TBG. The structural reconstruction suppresses the formation of the\nemergent Kagome lattice in the tiny-angle TBG. However, for the TBG around\nmagic angle, the sample-wide electronic Kagome lattices with tunable lattice\nconstants are directly imaged by using scanning tunneling microscope. Our\nobservations open a new direction to explore exotic correlated phases in moire\nsystems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Vacuum Thermal Switch Made of Phase Transition Materials Considering\n  Thin Film and Substrate Effects: In the present study, we demonstrate a vacuum thermal switch based on\nnear-field thermal radiation between phase transition materials, i.e., vanadium\ndioxide (VO2), whose phase changes from insulator to metal at 341 K. Similar\nmodulation effect has already been demonstrated and it will be extended to\nthin-film structure with substrate in this paper. Strong coupling of surface\nphonon polaritons between two insulating VO2 plates significantly enhances the\nnear-field heat flux, which on the other hand is greatly reduced when the VO2\nemitter becomes metallic, resulting strong thermal switching effect.\nFluctuational electrodynamics predicts more than 80% heat transfer reduction at\nsub-30-nm vacuum gaps and 50% at vacuum gap of 1 micron. By replacing the bulk\nVO2 receiver with a thin film of several tens of nanometers, the switching\neffect can be further improved over a broad range of vacuum gaps from 10 nm to\n1 um. In addition, for the purpose of more practical setup in experiments and\napplications, the SiO2 substrate effect is also considered for the structure\nwith thin-film emitter or receiver.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic bandstructure and van der Waals coupling of ReSe2 revealed by\n  high-resolution angle-resolved photoemission spectroscopy: ReSe2 and ReS2 are unusual compounds amongst the layered transition metal\ndichalcogenides as a result of their low symmetry, with a characteristic\nin-plane anisotropy due to in-plane rhenium chains. They preserve inversion\nsymmetry independent of the number of layers and, in contrast to more\nwell-known transition metal dichalcogenides, bulk and few-monolayer Re-TMD\ncompounds have been proposed to behave as electronically and vibrational\ndecoupled layers. Here, we probe for the first time the electronic band\nstructure of bulk ReSe2 by direct nanoscale angle-resolved photoemission\nspectroscopy. We find a highly anisotropic in- and out-of-plane electronic\nstructure, with the valence band maxima located away from any particular\nhigh-symmetry direction. The effective mass doubles its value perpendicular to\nthe Re chains and the interlayer van der Waals coupling generates significant\nelectronic dispersion normal to the layers. Our density functional theory\ncalculations, including spin-orbit effects, are in excellent agreement with\nthese experimental findings.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fabry-Perot interferometry at the $\u03bd$ = 2/5 fractional quantum Hall\n  state: Electronic Fabry-P{\\'e}rot interferometry is a powerful method to probe\nquasiparticle charge and anyonic braiding statistics in the fractional quantum\nHall regime. We extend this technique to the hierarchy $\\nu = 2/5$ fractional\nquantum Hall state, possessing two edge modes that in our device can be\ninterfered independently. The outer edge mode exhibits interference similar to\nthe behavior observed at the $\\nu = 1/3$ state, indicating that the outer edge\nmode at $\\nu = 2/5$ has properties similar to the single mode at $\\nu = 1/3$.\nThe inner mode shows an oscillation pattern with a series of discrete phase\njumps indicative of distinct anyonic braiding statistics. After taking into\naccount the impact of bulk-edge coupling, we extract an interfering\nquasiparticle charge ${e^*} = 0.17 \\pm 0.02$ and anyonic braiding phase $\\theta\n_a = (-0.43 \\pm 0.05)\\times 2\\pi$, which serve as experimental verification of\nthe theoretically predicted values of $e^* = \\frac{1}{5}$ and $\\theta _a =\n-\\frac{4\\pi}{5}$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Disorder-driven exceptional lines and Fermi ribbons in tilted nodal-line\n  semimetals: We consider the impact of disorder on the spectrum of three-dimensional\nnodal-line semimetals. We show that the combination of disorder and a tilted\nspectrum naturally leads to a non-Hermitian self-energy contribution that can\nsplit a nodal line into a pair of exceptional lines. These exceptional lines\nform the boundary of an open and orientable bulk Fermi ribbon in reciprocal\nspace on which the energy gap vanishes. We find that the orientation and shape\nof such a disorder-induced bulk Fermi ribbon is controlled by the tilt\ndirection and the disorder properties, which can also be exploited to realize a\ntwisted bulk Fermi ribbon with nontrivial winding number. Our results put\nforward a paradigm for the exploration of non-Hermitian topological phases of\nmatter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport in a Dissipative Luttinger Liquid: We study theoretically the transport through a single impurity in a\none-channel Luttinger liquid coupled to a dissipative (ohmic) bath . For\nnon-zero dissipation $\\eta$ the weak link is always a relevant perturbation\nwhich suppresses transport strongly. At zero temperature the current voltage\nrelation of the link is $I\\sim \\exp(-E_0/eV)$ where $E_0\\sim\\eta/\\kappa$ and\n$\\kappa$ denotes the compressibility. At non-zero temperature $T$ the linear\nconductance is proportional to $\\exp(-\\sqrt{{\\cal C}E_0/k_BT})$. The decay of\nFriedel oscillation saturates for distance larger than $L_{\\eta}\\sim 1/\\eta $\nfrom the impurity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum size phenomena in single-crystalline bismuth nanostructures: Size-dependent quantization of energy spectrum of conducting electrons in\nsolids leads to oscillating dependence of electronic properties on\ncorresponding dimension(s). In conventional metals with typical energy Fermi\nEF~1 eV and the charge carrier's effective masses m* of the order of free\nelectron mass m0, the quantum size phenomena provide noticeable impact only at\nnanometer scales. Here we experimentally demonstrate that in single-crystalline\nsemimetal bismuth nanostructures the electronic conductivity non-monotonously\ndecreases with reduction of the effective diameter. In samples grown along the\nparticular crystallographic orientation the electronic conductivity abruptly\nincreases at scales of about 50 nm due to metal-to-insulator transition\nmediated by the quantum confinement effect. The experimental findings are in\nreasonable agreement with theory predictions. The quantum-size phenomena should\nbe taken into consideration to optimize operation of the next generation of\nultra-small quantum nanoelectronic circuits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The influence of a strong infrared radiation field on the conductance\n  properties of doped semiconductors: This work presents an analytic angular differential cross section formula for\nthe electromagnetic radiation field assisted electron scattering by %% was on\nimpurities in semiconductors. These impurities are approximated with various\nmodel potentials. The scattered electrons are described by the well-known\nVolkov wave function, which has been used describe strong laser field matter\ninteraction for more than half a century, %% I would remove this time reference\nfor clarity which exactly describes the interaction of the electron with the\nexternal oscillating field. These calculations show that the electron\nconductance in a semiconductor could be enhanced by an order of magnitude if an\ninfrared electromagnetic field is present with $ 10^{11} < I < 10^{13}$\nW/cm$^2$ intensity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin current generation and control in carbon nanotubes by combining\n  rotation and magnetic field: We study the quantum dynamics of ballistic electrons in rotating carbon\nnanotubes in the presence of a uniform magnetic field. When the field is\nparallel to the nanotube axis, the rotation-induced electric field brings about\nthe spin-orbit interaction which, together with the kinetic, inertial, and\nZeeman terms, compose the Schr\\\"odinger-Pauli Hamiltonian of the system. Full\ndiagonalization of this Hamiltonian yields the eigenstates and eigenenergies\nleading to the calculation of the charge and spin currents. Our main result is\nthe demonstration that, by suitably combining the applied magnetic field\nintensity and rotation speed, one can tune one of the currents to zero while\nkeeping the other one finite, giving rise to a spin current generator.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Atomistic Simulation of Phonon and Magnon Thermal Transport across the\n  Ferro-Paramagnetic Transition: A temperature-dependent approach involving Green-Kubo equilibrium atomic and\nspin dynamics (GKEASD) is reported to assess phonon and magnon thermal\ntransport processes accounting for phonon-magnon interactions. Using\nbody-center cubic (BCC) iron as a case study, GKEASD successfully reproduces\nits characteristic temperature-dependent spiral and lattice thermal\nconductivities. The non-electronic thermal conductivity, i.e., the sum of\nphonon and magnon thermal conductivities, calculated using GKEASD for BCC Fe\nagrees well with experimental measurements. Spectral energy analysis reveals\nthat high-frequency phonon-magnon scattering rates are one order of magnitude\nlarger than those at low frequencies due to energy scattering conservation\nrules and high densities of states. Higher temperatures further accentuate this\nphenomenon. This new framework fills existing gaps in simulating thermal\ntransport across the ferro- to para-magnetic transition. Future application of\nthis methodology to phonon- and magnon-dominant insulators and semiconductors\nwill enhance understanding of emerging thermoelectric, spin caloritronic and\nsuperconducting materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Theoretical methods for excitonic physics in two-dimensional materials: In this tutorial we introduce the reader to several theoretical methods of\ndetermining the exciton wave functions and the corresponding eigenenergies. The\nmethods covered are either analytical, semi-analytical, or numeric. We make\nexplicit all the details associated with the different methods, thus allowing\nnewcomers to do research on their own, without experiencing a steep learning\ncurve. The tutorial starts with a variational method and ends with a simple\nsemi-analytical approach to solve the Bethe-Salpeter equation in\ntwo-dimensional (2D) gapped materials. For the first methods addressed in this\ntutorial, we focus on a single layer of hexagonal Boron Nitride (hBN) and of\ntransition metal dichalcogenide (TMD), as these are exemplary materials in the\nfield of 2D excitons. For explaining the Bethe- Salpeter method we choose the\nbiased bilayer graphene, which presents a tunnable band gap. The system has the\nright amount of complexity (without being excessive). This allows the\npresentation of the solution of the Bethe-Salpeter equation in a context that\ncan be easily generalized to more complex systems or to apply it to simpler\nmodels.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Superlattice of resonators on monolayer graphene created by intercalated\n  gold nanoclusters: Here we report on a \"new\" type of ordering which allows to modify the\nelectronic structure of a graphene monolayer (ML). We have intercalated small\ngold clusters between the top monolayer graphene and the buffer layer of\nepitaxial graphene. We show that these clusters perturb the quasiparticles on\nthe ML graphene, and act as quantum dots creating a superlattice of resonators\non the graphene ML, as revealed by a strong pattern of standing waves. A\ndetailed analysis of the standing wave patterns using Fourier Transform\nScanning Tunneling Spectroscopy strongly indicates that this phenomenon can\narise from a strong modification of the band structure of graphene and (or)\nfrom Charge Density Waves (CDW)where a large extension of Van Hove\nsingularities are involved.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "QED with magnetic textures: Coherent exchange between photons and different matter excitations (like\nqubits, acoustic surface waves or spins) allows for the entanglement of light\nand matter and provides a toolbox for performing fundamental quantum physics.\nOn top of that, coherent exchange is a basic ingredient in the majority of\nquantum information processors. In this work, we develop the theory for\ncoupling between magnetic textures (vortices and skyrmions) stabilized in\nferromagnetic nanodiscs and photons generated in a circuit. In particular, we\nshow how to perform broadband spectroscopy of the magnetic textures by sending\nphotons through a transmission line and recording the transmission. We also\ndiscuss the possibility of reaching the strong coupling regime between these\ntexture excitations and a single photon residing in a cavity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Self-consistent multi-mode lasing theory for complex or random lasing\n  media: A semiclassical theory of single and multi-mode lasing is derived for open\ncomplex or random media using a self-consistent linear response formulation.\nUnlike standard approaches which use closed cavity solutions to describe the\nlasing modes, we introduce an appropriate discrete basis of functions which\ndescribe also the intensity and angular emission pattern outside the cavity.\nThis constant flux (CF) basis is dictated by the Green function which arises\nwhen formulating the steady state Maxwell-Bloch equations as a self-consistent\nlinear response problem. This basis is similar to the quasi-bound state basis\nwhich is familiar in resonator theory and it obeys biorthogonality relations\nwith a set of dual functions. Within a single-pole approximation for the Green\nfunction the lasing modes are proportional to these CF states and their\nintensities and lasing frequencies are determined by a set of non-linear\nequations. When a near threshold approximation is made to these equations a\ngeneralized version of the Haken-Sauermann equations for multi-mode lasing is\nobtained, appropriate for open cavities. Illustrative results from these\nequations are given for single and few mode lasing states, for the case of\ndielectric cavity lasers. The standard near threshold approximation is found to\nbe unreliable. Applications to wave-chaotic cavities and random lasers are\ndiscussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport measurements on van der Waals heterostructures under pressure: The interlayer coupling, which has a strong influence on the properties of\nvan der Waals heterostructures, strongly depends on the interlayer distance.\nAlthough considerable theoretical interest has been demonstrated, experiments\nexploiting a variable interlayer coupling on nanocircuits are scarce due to the\nexperimental difficulties. Here, we demonstrate a novel method to tune the\ninterlayer coupling using hydrostatic pressure by incorporating van der Waals\nheterostructure based nanocircuits in piston-cylinder hydrostatic pressure\ncells with a dedicated sample holder design. This technique opens the way to\nconduct transport measurements on nanodevices under pressure using up to 12\ncontacts without constraints on the sample at fabrication level. Using\ntransport measurements, we demonstrate that hexagonal boron nitride capping\nlayer provides a good protection of van der Waals heterostructures from the\ninfluence of the pressure medium, and we show experimental evidence of the\ninfluence of pressure on the interlayer coupling using weak localization\nmeasurements on a TMDC/graphene heterostructure.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "$\\mathcal{PT}$-symmetric non-Hermitian Dirac semimetals: Parity-time ($\\mathcal{PT}$) symmetry plays an important role both in\nnon-Hermitian and topological systems. In non-Hermitian systems $\\mathcal{PT}$\nsymmetry can lead to an entirely real energy spectrum, while in topological\nsystems $\\mathcal{PT}$ symmetry gives rise to stable and protected Dirac\npoints. Here, we study a $\\mathcal{PT}$-symmetric system which is both\nnon-Hermitian and topological, namely a $\\mathcal{PT}$-symmetric Dirac\nsemimetal with non-Hermitian perturbations in three dimensions. We find that,\nin general, there are only two types of symmetry allowed non-Hermitian\nperturbations, namely non-Hermitian kinetic potentials, and non-Hermitian\nanti-commuting potentials. For both of these non-Hermitian potentials we\ninvestigate the band topology for open and periodic boundary conditions,\ndetermine the exceptional points, and compute the surface states. We find that\nwith periodic boundary conditions, the non-Hermitian kinetic potential leads to\nexceptional rings, while the non-Hermitian anti-commuting potential generates\nexceptional spheres, which separate regions with broken $\\mathcal{PT}$ symmetry\nfrom regions with unbroken $\\mathcal{PT}$ symmetry. With open boundary\nconditions, the non-Hermitian kinetic potential induces a non-Hermitian skin\neffect which is localized on both sides of the sample due to symmetry, while\nthe non-Hermitian anticommuting potential leads to Fermi ribbon surface states.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Inelastic Cotunneling Resonances in the Coulomb-Blockade Transport in\n  Donor-Atom Transistors: We report finite-bias characteristics of electrical transport through\nphosphorus donors in silicon nanoscale transistors, in which we observe\ninelastic-cotunneling current in the Coulomb blockade region. The cotunneling\ncurrent appears like a resonant-tunneling current peak emerging from the\nexcited state at the crossover between blockade and non-blockade regions. These\ncotunneling features are unique, since the inelastic-cotunneling currents have\nso far been reported either as a broader hump or as a continuous increment of\ncurrent. This finding is ascribed purely due to excitation-related inelastic\ncotunneling involving the ground and excited states. Theoretical calculations\nwere performed for a two-level quantum dot, supporting our experimental\nobservation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Unconventional transformation of spin Dirac phase across a topological\n  quantum phase transition: The topology of a topological material can be encoded in its surface states.\nThese surface states can only be removed by a bulk topological quantum phase\ntransition into a trivial phase. Here we use photoemission spectroscopy to\nimage the formation of protected surface states in a topological insulator as\nwe chemically tune the system through a topological transition. Surprisingly,\nwe discover an exotic spin-momentum locked, gapped surface state in the trivial\nphase that shares many important properties with the actual topological surface\nstate in anticipation of the change of topology. Using a spin-resolved\nmeasurement, we show that apart from a surface band-gap these states develop\nspin textures similar to the topological surface states well-before the\ntransition. Our results offer a general paradigm for understanding how surface\nstates in topological phases arise and are suggestive for future realizing Weyl\narcs, condensed matter supersymmetry and other fascinating phenomena in the\nvicinity of topological quantum criticality.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-polarized quantum transport through a T-shape quantum dot-array: a\n  model of spin splitter: We in this paper study theoretically the spin-polarized quantum transport\nthrough a T-shape quantum dot-array by means of transfer-matrix method along\nwith the Green^{,}s function technique. Multi-magnetic fields are used to\nproduce the spin-polarized transmission probabilities and therefore the spin\ncurrents, which are shown to be tunable in a wide range by adjusting the\nenergy, and the direction-angle of magnetic fields as well. Particularly the\nopposite- spin- polarization currents separately flowing out to two electrodes\ncan be generated and thus the system acts as a spin splitter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spontaneous spin polarization in quantum point contacts: We use spatial spin separation by a magnetic focusing technique to probe the\npolarization of quantum point contacts. The point contacts are fabricated from\np-type GaAs/AlGaAs heterostructures. A finite polarization is measured in the\nlow-density regime, when the conductance of a point contact is tuned to\n<2e^2/h. Polarization is stronger in samples with a well defined ``0.7\nstructure''",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effects of bonding type and interface geometry on coherent transport\n  through the single-molecule magnet Mn12: We examine theoretically coherent electron transport through the\nsingle-molecule magnet Mn$_{12}$, bridged between Au(111) electrodes, using the\nnon-equilibrium Green's function method and the density-functional theory. We\nanalyze the effects of bonding type, molecular orientation, and geometry\nrelaxation on the electronic properties and charge and spin transport across\nthe single-molecule junction. We consider nine interface geometries leading to\nfive bonding mechanisms and two molecular orientations: (i) Au-C bonding, (ii)\nAu-Au bonding, (iii) Au-S bonding, (iv) Au-H bonding, and (v) physisorption via\nvan der Waals forces. The two molecular orientations of Mn$_{12}$ correspond to\nthe magnetic easy axis of the molecule aligned perpendicular [hereafter denoted\nas orientation (1)] or parallel [orientation (2)] to the direction of electron\ntransport. We find that the electron transport is carried by the lowest\nunoccupied molecular orbital (LUMO) level in all the cases that we have\nsimulated. Relaxation of the junction geometries mainly shifts the relevant\noccupied molecular levels toward the Fermi energy as well as slightly reduces\nthe broadening of the LUMO level. As a result, the current slightly decreases\nat low bias voltage. Our calculations also show that placing the molecule in\nthe orientation (1) broadens the LUMO level much more than in the orientation\n(2), due to the internal structure of the Mn$_{12}$. Consequently, junctions\nwith the former orientation yield a higher current than those with the latter.\nAmong all of the bonding types considered, the Au-C bonding gives rise to the\nhighest current (about one order of magnitude higher than the Au-S bonding),\nfor a given distance between the electrodes. The current through the junction\nwith other bonding types decreases in the order of Au-Au, Au-S, and Au-H.\nImportantly, the spin-filtering effect in all the nine geometries stays robust\nand their ratios of the majority-spin to the minority-spin transmission\ncoefficients are in the range of 10$^3$ to 10$^8$. The general trend in\ntransport among the different bonding types and molecular orientations obtained\nfrom this study may be applied to other single-molecular magnets.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magically strained bilayer graphene with flat bands: Twist bilayer graphenes with magical angle have nearly flat band, which\nbecome strongly correlated electron systems. Herein, we propose another system\nbased on strained bilayer graphene that have flat band at the intrinsic Fermi\nlevel. The top and bottom layers are uniaxially stretched along different\ndirections. When the strength and directions of the strain satisfy certain\ncondition, the periodical lattices of the two layers are commensurate to each\nother. The regions with AA, AB and BA stacking arrange in a triangular lattice.\nWith magical strain, the bands around the intrinsic Fermi level are nearly flat\nand have large gap from the other bands. This system could provide more\nfeasible platform for graphene-based integrated electronic system with\nsuperconductivity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Maxwell's demon in a double quantum dot with continuous charge detection: Converting information into work has during the last decade gained renewed\ninterest as it gives insight into the relation between information theory and\nthermodynamics. Here we theoretically investigate an implementation of\nMaxwell's demon in a double quantum dot and demonstrate how heat can be\nconverted into work using only information. This is accomplished by\ncontinuously monitoring the charge state of the quantum dots and transferring\nelectrons against a voltage bias using a feedback scheme. We investigate the\nelectrical work produced by the demon and find a non-Gaussian work\ndistribution. To illustrate the effect of a realistic charge detection scheme,\nwe develop a model taking into account noise as well as a finite delay time,\nand show that an experimental realization is feasible with present day\ntechnology. Depending on the accuracy of the measurement, the system is\noperated as an implementation of Maxwell's demon or a single-electron pump.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-Orbit gauge and quantum spin Hall effect: We have shown that the non-Abelian spin-orbit gauge field strength of the\nRashba and Dresselhaus interactions, when split into two Abelian field\nstrengths, the Hamiltonian of the system can be re-expressed as a Landau level\nproblem with a particular relation between the two coupling parameters. The\nquantum levels are created with up and down spins with opposite chirality and\nleads to the quantum spin Hall effect.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Detecting magneto-optical interactions in nanostructures: Effects due to magneto-optical interactions are responsible for most of the\nphenomena discovered in optoelectronics and spintronics. Magneto-optical\ninteractions can generate elementary excitations of the order of light-magnetic\nmatter, which can flow under certain conditions. Here, we observe the\nintensities of magneto-optical interactions in hexagonal arrays of magnetic\nnanowires using experimental measurements and simulations. Nanowires of three\nmaterials (cobalt-Co, iron-Fe, and nickel-Ni) were electrodeposited on alumina\nmembranes by the AC electrodeposition method. Our results reveal that the\nmagneto-optical behavior can produce, under certain conditions, a kind of\navalanche of magneto-optical interactions, which is dynamic. Such an\nobservation shows the possibility of generating a magneto-optical current\n(spin-opto current).",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Delta-T noise for fractional quantum Hall states at different filling\n  factor: The current fluctuations due to a temperature bias, i.e. the delta-$T$ noise,\nallow one to access properties of strongly interacting systems which cannot be\naddressed by the usual voltage-induced noise. In this work, we study the full\ndelta-$T$ noise between two different fractional quantum Hall edge states, with\nfilling factors $(\\nu_L,\\nu_R)$ in the Laughlin sequence, coupled through a\nquantum point contact and connected to two reservoirs at different\ntemperatures. We are able to solve exactly the problem for all couplings and\nfor any set of temperatures in the specific case of an hybrid junction\n$(1/3,1)$. Moreover, we derive a universal analytical expression which connects\nthe delta-$T$ noise to the equilibrium one valid for all generic pairs\n$(\\nu_L,\\nu_R)$ up to the first order in the temperature mismatch. We expect\nthat the linear term can be accessible in nowadays experimental set-ups. We\ndescribe the two opposite coupling regimes focusing on the strong one which\ncorrespond to a non-trivial situation. Our analysis on delta-$T$ noise allows\nus to better understand the transport properties of strongly interacting\nsystems and to move toward more involved investigation concerning the\nstatistics and scaling dimension of their emergent excitations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The spin Hall effect: In metallic systems with spin-orbit coupling a longitudinal charge current\nmay generate a transverse pure spin current; vice-versa an injected pure spin\ncurrent may result in a transverse charge current. Such direct and inverse spin\nHall effects share the same microscopic origin: intrinsic band/device structure\nproperties, external factors such as impurities, or a combination of both. They\nallow all-electrical manipulation of the electronic spin degrees of\nfreedom,i.e. without magnetic elements, and their transverse nature makes them\npotentially dissipationless. It is customary to talk of spin Hall effects in\nplural form, referring to a group of related phenomena typical of spin-orbit\ncoupled systems of lowered symmetry.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum many-body simulation using monolayer exciton-polaritons in\n  coupled-cavities: Quantum simulation is a promising approach to understand complex strongly\ncorrelated many-body systems using relatively simple and tractable systems.\nPhoton-based quantum simulators have great advantages due to the possibility of\ndirect measurements of multi-particle correlations and ease of simulating\nnon-equilibrium physics. However, interparticle interaction in existing\nphotonic systems is often too weak limiting the potential of quantum\nsimulation. Here we propose an approach to enhance the interparticle\ninteraction using exciton-polaritons in MoS$_2$ monolayer quantum-dots embedded\nin 2D photonic crystal microcavities. Realistic calculation yields optimal\nrepulsive interaction in the range of $1$-$10$~meV --- more than an order of\nmagnitude greater than the state-of-art value. Such strong repulsive\ninteraction is found to emerge neither in the photon-blockade regime for small\nquantum dot nor in the polariton-blockade regime for large quantum dot, but in\nthe crossover between the two regimes with a moderate quantum-dot radius around\n20~nm. The optimal repulsive interaction is found to be largest in MoS$_2$\namong commonly used optoelectronic materials. Quantum simulation of strongly\ncorrelated many-body systems in a finite chain of coupled cavities and its\nexperimental signature are studied via exact diagonalization of the many-body\nHamiltonian. A method to simulate 1D superlattices for interacting\nexciton-polariton gases in serially coupled cavities is also proposed.\nRealistic considerations on experimental realizations reveal advantages of\ntransition metal dichalcogenide monolayer quantum-dots over conventional\nsemiconductor quantum-emitters.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Analytic approach to the edge state of the Kane-Mele Model: We investigate the edge state of a two-dimensional topological insulator\nbased on the Kane-Mele model. Using complex wave numbers of the Bloch wave\nfunction, we derive an analytical expression for the edge state localized near\nthe edge of a semi-infinite honeycomb lattice with a straight edge. For the\ncomparison of the edge type effects, two types of the edges are considered in\nthis calculation; one is a zigzag edge and the other is an armchair edge. The\ncomplex wave numbers and the boundary condition give the analytic equations for\nthe energies and the wave functions of the edge states. The numerical solutions\nof the equations reveal the intriguing spatial behaviors of the edge state. We\ndefine an edge-state width for analyzing the spatial variation of the\nedge-state wave function. Our results show that the edge-state width can be\neasily controlled by a couple of parameters such as the spin-orbit coupling and\nthe sublattice potential. The parameter dependences of the edge-state width\nshow substantial differences depending on the edge types. These demonstrate\nthat, even if the edge states are protected by the topological property of the\nbulk, their detailed properties are still discriminated by their edges. This\nedge dependence can be crucial in manufacturing small-sized devices since the\nlength scale of the edge state is highly subject to the edges.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Unravelling the electrical properties of epitaxial Graphene nanoribbons: The size-dependent electrical resistivity of single-layer graphene ribbons\nhas been studied experimentally for ribbon widths from 16 nm to 320 nm. The\nexperimental findings are that the resistivity follows a more dramatic trend\nthan that seen for metallic nanowires of similar dimensions, due to a\ncombination of surface scattering from the edges, band-gap related effects and\nshifts in the Fermi level due to edge effects. We show that the Charge\nNeutrality point switches polarity below a ribbon width of around 50 nm, and\nthat at this point, the thermal coefficient of resistance is a maximum. The\nmajority doping type therefore can be controlled by altering ribbon width. We\nalso demonstrate that an alumina passivation layer has a significant effect on\nthe mean free path of the charge carriers within the graphene, which can be\nprobed directly via measurements of the width-dependent resistivity. We propose\na model for conduction that takes edge and confinement effects into account.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical manipulation of nuclear spin by a two-dimensional electron gas: Conduction electrons are used to optically polarize, detect and manipulate\nnuclear spin in a (110) GaAs quantum well. Using optical Larmor magnetometry,\nwe find that nuclear spin can be polarized along or against the applied\nmagnetic field, depending on field polarity and tilting of the sample with\nrespect to the optical pump beam. Periodic optical excitation of the\nquantum-confined electron spin reveals a complete spectrum of optically-induced\nand quadrupolar-split nuclear resonances, as well as evidence for delta m = 2\ntransitions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Classification of Exceptional Nodal Topologies Protected by\n  $\\mathcal{PT}$ Symmetry: Exceptional degeneracies, at which both eigenvalues and eigenvectors\ncoalesce, and parity-time ($\\mathcal{PT}$) symmetry, reflecting balanced gain\nand loss in photonic systems, are paramount concepts in non-Hermitian systems.\nWe here complete the topological classification of exceptional nodal\ndegeneracies protected by $\\mathcal{PT}$ symmetry in up to three dimensions and\nprovide simple example models whose exceptional nodal topologies include\npreviously overlooked possibilities such as second-order knotted surfaces of\narbitrary genus, third-order knots and fourth-order points.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamical characterization of Weyl nodes in Floquet Weyl semimetal\n  phases: Due to studies in nonequilibrium (periodically-driven) topological matter, it\nis now understood that some topological invariants used to classify equilibrium\nstates of matter do not suffice to describe their nonequilibrium counterparts.\nIndeed, in Floquet systems the additional gap arising from the periodicity of\nthe quasienergy Brillouin zone often leads to unique topological phenomena\nwithout equilibrium analogues. In the context of Floquet Weyl semimetal, Weyl\npoints may be induced at both quasienergy zero and $\\pi/T$ ($T$ being the\ndriving period) and these two types of Weyl points can be very close to each\nother in the momentum space. Because of their momentum-space proximity, the\nchirality of each individual Weyl point may become hard to characterize in both\ntheory and experiments, thus making it challenging to determine the system's\noverall topology. In this work, inspired by the construction of dynamical\nwinding numbers in Floquet Chern insulators, we propose a dynamical invariant\ncapable of characterizing and distinguishing between Weyl points at different\nquasienergy values, thus advancing one step further in the topological\ncharacterization of Floquet Weyl semimetals. To demonstrate the usefulness of\nsuch a dynamical topological invariant, we consider a variant of the\nperiodically kicked Harper model (the very first model in studies of Floquet\ntopological phases) that exhibits many Weyl points, with the number of Weyl\npoints rising unlimitedly with the strength of some system parameters.\nFurthermore, we investigate the two-terminal transport signature associated\nwith the Weyl points. Theoretical findings of this work pave the way for\nexperimentally probing the rich topological band structures of some seemingly\nsimple Floquet semimetal systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron transport through molecular bridge systems: Electron transport characteristics are investigated through some molecular\nchains attached to two non-superconducting electrodes by the use of Green's\nfunction method. Here we do parametric calculations based on the tight-binding\nformulation to characterize the electron transport through such bridge systems.\nThe transport properties are significantly influenced by (a) the length of the\nmolecular chain and (b) the molecule-to-electrodes coupling strength and here\nwe focus are results in these aspects. In this context we also discuss the\nsteady state current fluctuations, the so-called shot noise, which is a\nconsequence of the quantization of charge and is not directly available through\nconductance measurements.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nonlocal Response and Anamorphosis: the Case of Few-Layer Black\n  Phosphorus: Few-layer black phosphorus was recently rediscovered as a narrow-bandgap\natomically thin semiconductor and has already attracted unprecedented attention\ndue to its interesting properties. One feature of this material that sets it\napart from other atomically thin crystals is its structural in-plane anisotropy\nwhich manifests in strongly anisotropic transport characteristics. However,\ntraditional angle-resolved conductance measurements present a challenge for\nnanoscale systems such as black phosphorus, calling for new approaches in\nprecision studies of transport anisotropy. Here we show that the nonlocal\nresponse, being exponentially sensitive to the anisotropy value, provides a\npowerful tool for determining the anisotropy. This is established by combining\nmeasurements of the orientation-dependent nonlocal resistance response with the\nanalysis based on the anamorphosis relations. We demonstrate that the nonlocal\nresponse can differ by orders of magnitude for different crystallographic\ndirections even when the anisotropy is at most order-one, allowing us to\nextract accurate anisotropy values.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnonic bending, phase shifting and interferometry in a 2D\n  reconfigurable nanodisk crystal: Strongly-interacting nanomagnetic systems are pivotal across next-generation\ntechnologies including reconfigurable magnonics and neuromorphic computation.\nControlling magnetisation state and local coupling between neighbouring\nnanoelements allows vast reconfigurable functionality and a host of associated\nfunctionalities. However, existing designs typically suffer from an inability\nto tailor inter-element coupling post-fabrication and nanoelements restricted\nto a pair of Ising-like magnetisation states. Here, we propose a new class of\nreconfigurable magnonic crystal incorporating nanodisks as the functional\nelement. Magnetic nanodisks are crucially bistable in macrospin and vortex\nstates, allowing inter-element coupling to be selectively activated (macrospin)\nor deactivated (vortex). Through microstate engineering, we leverage the\ndistinct coupling behaviours and magnonic band structures of bistable nanodisks\nto achieve reprogrammable magnonic waveguiding, bending, gating and\nphase-shifting across a 2D network. The potential of nanodisk-based magnonics\nfor wave-based computation is demonstrated via an all-magnon interferometer\nexhibiting XNOR logic functionality. Local microstate control is achieved here\nvia topological magnetic writing using a magnetic force microscope tip.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Continuum model for chiral induced spin selectivity in helical molecules: A minimal model is exactly solved for electron spin transport on a helix.\nElectron transport is assumed to be supported by well oriented $p_z$ type\norbitals on base molecules forming a staircase of definite chirality. In a\ntight binding interpretation, the SOC opens up an effective $\\pi_z-\\pi_z$\ncoupling via interbase $p_{x,y}-p_z$ hopping, introducing spin coupled\ntransport. The resulting continuum model spectrum shows two Kramers doublet\ntransport channels with a gap proportional to the SOC. Each doubly degenerate\nchannel satisfies time reversal symmetry, nevertheless, a bias chooses a\ntransport direction and thus selects for spin orientation. The model predicts\nwhich spin orientation is selected depending on chirality and bias, changes in\nspin preference as a function of input Fermi level and scattering suppression\nprotected by the SO gap. We compute the spin current with a definite helicity\nand find it to be proportional to the torsion of the chiral structure and the\nnon-adiabatic Aharonov- Anandan phase. To describe room temperature transport\nwe assume that the total transmission is the result of a product of coherent\nsteps limited by the coherence length.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Pauli spin blockade in weakly coupled quantum dots: In a two-level system, constituted by two serially coupled single level\nquantum dots, coupled to external leads we find that the current is suppressed\nin one direction of biasing caused by a fully occupied two-electron triplet\nstate in the interacting region. The efficiency of the current suppression is\ngoverned by the ratio between the interdot tunnelling rate and the level\noff-set. In the opposite bias direction, the occupation of the two-electron\ntriplet is lifted which allows a larger current to flow through the system,\nwhere the conductance is provided by transitions between one-electron states\nand two-electron singlet states. Is is also shown that a finite ferromagnetic\ninterdot exchange interaction provides an extended range of the current\nsuppression, while an anti-ferromagnetic exchange leads to a decreased range of\nthe blockade regime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Charge Relaxation and Dephasing in Coulomb Coupled Conductors: The dephasing time in coupled mesoscopic conductors is caused by the\nfluctuations of the dipolar charge permitted by the long range Coulomb\ninteraction. We relate the phase breaking time to elementary transport\ncoefficients which describe the dynamics of this dipole: the capacitance, an\nequilibrium charge relaxation resistance and in the presence of transport\nthrough one of the conductors a non-equilibrium charge relaxation resistance.\nThe discussion is illustrated for a quantum point contact in a high magnetic\nfield in proximity to a quantum dot.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spatial patterns of dissipative polariton solitons in semiconductor\n  microcavities: Semiconductor microcavities operating in the polaritonic regime are highly\nnon-linear, high speed systems due to the unique half-light, half-matter nature\nof polaritons. Here, we report for the first time the observation of\npropagating multi-soliton polariton patterns consisting of multi-peak\nstructures either along (x) or perpendicular to (y) the direction of\npropagation. Soliton arrays of up to 5 solitons are observed, with the number\nof solitons controlled by the size or power of the triggering laser pulse. The\nbreak-up along the x direction occurs due to interplay of bistability, negative\neffective mass and polariton-polariton scattering, while in the y direction the\nbreak-up results from nonlinear phase-dependent interactions of propagating\nfronts. We show the experimental results are in good agreement with numerical\nmodelling. Our observations are a step towards ultrafast all-optical signal\nprocessing using sequences of solitons as bits of information.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Reversible edge spin currents in antiferromagnetically proximitized\n  dichalcogenides: We explore proximity effects on transition metal dichalcogenide ribbons\ndeposited on antiferromagnetic (AFM) insulating substrates. We model these\nhybrid heterostructures using a tight-binding model that incorporates exchange\nand Rashba fields induced by proximity to the AFM material. The robust edge\nstates that disperse in the midgap of the dichalcogenide are strongly affected\nby induced exchange fields that reflect different AFM ordering in the\nsubstrate. This results in enhanced spin-orbit coupling effects and complex\nspin projection content for states on zigzag ribbon edges. Gated systems that\nshift the Fermi level in the midgap range are also shown to exhibit spin\npolarized currents on these edges. Antiparallel exchange fields along the edge\nresults in spin currents that can reverse polarization with the applied field.\nThe added functionality of these hybrid structures can provide spintronic\ndevices and versatile platforms to further exploit proximity effects in diverse\nmaterial systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Arbitrary qubit transformations on tuneable Rashba rings: An exact solution is presented for the time-dependent wavefunction of a\nKramers doublet which propagates around a quantum ring with tuneable Rashba\nspin-orbit interaction. By propagating in segments it is shown that\nKramers-doublet qubits may be defined for which transformations on the Bloch\nsphere may be performed for an integral number of revolutions around the ring.\nThe conditions for full coverage of the Bloch sphere are determined and\nexplained in terms of sequential qubit rotations due to electron motion along\nthe segments, with change of rotation axes between segments due to adiabatic\nchanges in the Rashba spin-orbit interaction. Prospects and challenges for\npossible realizations are discussed for which rings based on InAs quantum wires\nare promising candidates.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current-induced switching in transport through anisotropic magnetic\n  molecules: Anisotropic single-molecule magnets may be thought of as molecular switches,\nwith possible applications to molecular spintronics. In this paper, we consider\ncurrent-induced switching in single-molecule junctions containing an\nanisotropic magnetic molecule. We assume that the carriers interact with the\nmagnetic molecule through the exchange interaction and focus on the regime of\nhigh currents in which the molecular spin dynamics is slow compared to the time\nwhich the electrons spend on the molecule. In this limit, the molecular spin\nobeys a non-equilibrium Langevin equation which takes the form of a generalized\nLandau-Lifshitz-Gilbert equation and which we derive microscopically by means\nof a non-equilibrium Born-Oppenheimer approximation. We exploit this Langevin\nequation to identify the relevant switching mechanisms and to derive the\ncurrent-induced switching rates. As a byproduct, we also derive S-matrix\nexpressions for the various torques entering into the Landau-Lifshitz-Gilbert\nequation which generalize previous expressions in the literature to\nnon-equilibrium situations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Control of nonlocal magnon spin transport via magnon drift currents: Spin transport via magnon diffusion in magnetic insulators is important for a\nbroad range of spin-based phenomena and devices. However, the absence of the\nmagnon equivalent of an electric force is a bottleneck. In this work, we\ndemonstrate the controlled generation of magnon drift currents in yttrium iron\ngarnet/platinum heterostructures. By performing electrical injection and\ndetection of incoherent magnons, we find magnon drift currents that stem from\nthe interfacial Dzyaloshinskii-Moriya interaction. We can further control the\nmagnon drift by the orientation of the magnetic field. The drift current\nchanges the magnon propagation length by up to $\\pm$ 6 % relative to diffusion.\nWe generalize the magnonic spin transport theory to include a finite drift\nvelocity resulting from any inversion asymmetric interaction, and obtain\nresults consistent with our experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dephasing by extremely dilute magnetic impurities revealed by\n  Aharonov-Bohm oscillations: We have probed the magnetic field dependence of the electron phase coherence\ntime $\\tau_\\phi$ by measuring the Aharonov-Bohm conductance oscillations of\nmesoscopic Cu rings. Whereas $\\tau_\\phi$ determined from the low-field\nmagnetoresistance saturates below 1 K, the amplitude of Aharonov-Bohm $h/e$\noscillations increases strongly on a magnetic field scale proportional to the\ntemperature. This provides strong evidence that a likely explanation for the\nfrequently observed saturation of $\\tau_\\phi$ at low temperature in weakly\ndisordered metallic thin films is the presence of extremely dilute magnetic\nimpurities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "States near Dirac points of rectangular graphene dot in a magnetic field: In neutral graphene dots the Fermi level coincides with the Dirac points. We\nhave investigated in the presence of a magnetic field several unusual\nproperties of single electron states near the Fermi level of such a\nrectangular-shaped graphene dot with two zigzag and two armchair edges. We find\nthat a quasi-degenerate level forms near zero energy and the number of states\nin this level can be tuned by the magnetic field. The wavefunctions of states\nin this level are all peaked on the zigzag edges with or without some weight\ninside the dot. Some of these states are magnetic field-independent surface\nstates while the others are field-dependent. We have found a scaling result\nfrom which the number of magnetic field-dependent states of large dots can be\ninferred from those of smaller dots.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Adiabatic and local approximations for the Kohn-Sham potential in\n  time-dependent Hubbard chains: We obtain the exact Kohn-Sham potentials $V_{\\mathrm{KS}}$ of time-dependent\ndensity-functional theory for 1D Hubbard chains, driven by a d.c.\\ external\nfield, using the time-dependent electron density and current density obtained\nfrom exact many-body time-evolution. The exact $V_{\\mathrm{xc}}$ is compared to\nthe adiabatically-exact $V_{\\mathrm{xc}}^{\\mathrm{ad}}$ and the \"instantaneous\nground state\" $V_{\\mathrm{xc}}^{\\mathrm{igs}}$. The latter is shown to work\neffectively in some cases when the former fails. Approximations for the\nexchange-correlation potential $V_{\\mathrm{xc}}$ and its gradient, based on the\nlocal density and on the local current density, are also considered and both\nphysical quantities are observed to be far outside the reach of any possible\nlocal approximation. Insight into the respective roles of ground-state and\nexcited-state correlation in the time-dependent system, as reflected in the\npotentials, is provided by the pair correlation function.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ultrafast Quantum-path Interferometry Revealing the Generation Process\n  of Coherent Phonons: Optical dual-pulse pumping actively creates quantum-mechanical superposition\nof the electronic and phononic states in a bulk solid. We here made transient\nreflectivity measurements in an n-GaAs using a pair of relative-phase-locked\nfemtosecond pulses and found characteristic interference fringes. This is a\nresult of quantum-path interference peculiar to the dual-pulse excitation as\nindicated by theoretical calculation. Our observation reveals that the pathway\nof coherent phonon generation in the n-GaAs is impulsive stimulated Raman\nscattering at the displaced potential due to the surface-charge field, even\nthough the photon energy lies in the opaque region.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Carbon nanotube: a low-loss spin-current waveguide: We demonstrate with a quantum-mechanical approach that carbon nanotubes are\nexcellent spin-current waveguides and are able to carry information stored in a\nprecessing magnetic moment for long distances with very little dispersion and\nwith tunable degrees of attenuation. Pulsed magnetic excitations are predicted\nto travel with the nanotube Fermi velocity and are able to induce similar\nexcitations in remote locations. Such an efficient way of transporting magnetic\ninformation suggests that nanotubes are promising candidates for memory devices\nwith fast magnetization switchings.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Imaging coherent electron wave flow in a two-dimensional electron gas: We measure the energy distribution of electrons passing through a\ntwo-dimensional electron gas using a scanning probe microscope. We present\ndirect spatial images of coherent electron wave flow from a quantum point\ncontact formed in a GaAs/AlGaAs two-dimensional electron gas using a liquid He\ncooled SPM. A negative voltage is placed on the tip, which creates a small\nregion of depleted electrons that backscatters electron waves. Oscillating the\nvoltage on the tip and locking into this frequency gives the spatial derivative\nof electron flow perpendicular to the direction of current flow. We show images\nof electron flow using this method. By measuring the amount of electrons\nbackscattered as a function of the voltage applied to the tip, the energy\ndistribution of electrons is measured.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magneto-resistance quantum oscillations in a magnetic two-dimensional\n  electron gas: Magneto-transport measurements of Shubnikov-de Haas (SdH) oscillations have\nbeen performed on two-dimensional electron gases (2DEGs) confined in CdTe and\nCdMnTe quantum wells. The quantum oscillations in CdMnTe, where the 2DEG\ninteracts with magnetic Mn ions, can be described by incorporating the\nelectron-Mn exchange interaction into the traditional Lifshitz-Kosevich\nformalism. The modified spin splitting leads to characteristic beating pattern\nin the SdH oscillations, the study of which indicates the formation of Mn\nclusters resulting in direct anti-ferromagnetic Mn-Mn interaction. The Landau\nlevel broadening in this system shows a peculiar decrease with increasing\ntemperature, which could be related to statistical fluctuations of the Mn\nconcentration.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Minigap and Andreev bound states in ballistic graphene: A finite-size normal conductor, proximity-coupled to a superconductor has\nbeen predicted to exhibit a so-called minigap, in which quasiparticle\nexcitations are prohibited. Here, we report on the direct observation of such a\nminigap in ballistic graphene, coupled to superconducting MoRe leads. The\nminigap is probed by finite bias spectroscopy through a weakly coupled junction\nin the graphene region and its value is given by the dimensions of the device.\nBesides the minigap, we observe a distinct peak in the differential resistance,\nwhich we attribute to weakly coupled Andreev bound states (ABS) located near\nthe superconductor-graphene interface. For weak magnetic fields, the phase\naccumulated in the normal-conducting region shifts the ABS in quantitative\nagreement with predictions from tight-binding calculations based on the\nBogolioubov-de Gennes equation as well as with an analytical semiclassical\nmodel.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Plasmonic Nanoantennas: We study plasmonic excitations in the limit of few electrons, in one-atom\nthick sodium chains, and characterize them based on collectivity. We also\ncompare the excitations to classical localised plasmon modes and find for the\nlongitudinal mode a quantum-classical transition around 10 atoms. The\ntransverse mode appears at much higher energies than predicted classically for\nall chain lengths. The electric field enhancement is also considered which is\nmade possible by considering the effects of electron-phonon coupling on the\nbroadening of the electronic spectra. Large field enhancements are possible on\nthe molecular level allowing us to consider the validity of using molecules as\nthe ultimate small size limit of plasmonic antennas. Additionally, we consider\nthe case of a dimer system of two sodium chains, where the gap can be\nconsidered as a picocavity, and we analyse the charge-transfer states and their\ndependence on the gap size as well as chain size. Our results and methods are\nuseful for understanding and developing ultra-small, tunable and novel\nplasmonic devices that utilise quantum effects that could have applications in\nquantum optics, quantum metamaterials, cavity-quantum electrodynamics and\ncontrolling chemical reactions, as well as deepening our understanding of\nlocalised plasmons in low dimensional molecular systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-singlet hierarchy in the fractional quantum Hall effect: We show that the so-called permanent quantum Hall states are formed by the\ninteger quantum Hall effects on the Haldane-Rezayi quantum Hall state. Novel\nconformal field theory description along with this picture is deduced. The odd\ndenominator plateaux observed around $\\nu=5/2$ are the permanent states if the\n$\\nu=5/2$ plateau is the Haldane-Rezayi state. We point out that there is no\nsuch hierarchy on other candidate states for $\\nu=5/2$. We propose experiments\nto test our prediction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Graphene Transistor as a Probe for Streaming Potential: We explore the dependence of electrical transport in a graphene field effect\ntransistor (GraFET) on the flow of the liquid within the immediate vicinity of\nthat transistor. We find large and reproducible shifts in the charge neutrality\npoint of GraFETs that are dependent on the fluid velocity and the ionic\nconcentration. We show that these shifts are consistent with the variation of\nthe local electrochemical potential of the liquid next to graphene that are\ncaused by the fluid flow (streaming potential). Furthermore, we utilize the\nsensitivity of electrical transport in GraFETs to the parameters of the fluid\nflow to demonstrate graphene-based mass flow and ionic concentration sensing.\nWe successfully detect a flow as small as~70nL/min, and detect a change in the\nionic concentration as small as ~40nM.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Photovoltaic performances in a cavity-coupled double quantum dots\n  photocell: Revealing the quantum regime of photovoltaics is crucial to enhancing the\ninternal quantum efficiency of a double quantum dots (DQDs) photocell housed in\na cavity. In this study, the performance of a quantum photovoltaic is evaluated\nbased on the current-voltage and power-voltage characteristics in a\ncavity-coupled DQDs photocell. The results show that the cavity-DQDs coupling\ncoefficient plays a dissipative role in the photovoltaic performance, and the\ncavity has a limited size for the photovoltaic performance. Additionally, more\nlow-energy photons are easily absorbed by this cavity-coupled DQDs photocell\ncompared with the case without cavity. These results may provide some\nstrategies for improving the photoelectric conversion efficiency and internal\nquantum efficiency of cavity-coupled DQDs photocells.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Superoperator nonequilibrium Green's function theory of many-body\n  systems; Applications to charge transfer and transport in open junctions: Nonequilibrium Green's functions provide a powerful tool for computing the\ndynamical response and particle exchange statistics of coupled quantum systems.\nWe formulate the theory in terms of the density matrix in Liouville space and\nintroduce superoperator algebra that greatly simplifies the derivation and the\nphysical interpretation of all quantities. Expressions for various observables\nare derived directly in real time in terms of superoperator nonequilibrium\nGreen's functions (SNGF), rather than the artificial time-loop required in\nSchwinger's Hilbert-space formulation. Applications for computing interaction\nenergies, charge densities, average currents, current induced fluorescence,\nelectroluminescence and current fluctuation (electron counting) statistics are\ndiscussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bichromatic Rabi control of semiconductor qubits: Electrically-driven spin resonance is a powerful technique for controlling\nsemiconductor spin qubits. However, it faces challenges in qubit addressability\nand off-resonance driving in larger systems. We demonstrate coherent\nbichromatic Rabi control of quantum dot hole spin qubits, offering a\nspatially-selective approach for large qubit arrays. By applying simultaneous\nmicrowave bursts to different gate electrodes, we observe multichromatic\nresonance lines and resonance anticrossings that are caused by the ac Stark\nshift. Our theoretical framework aligns with experimental data, highlighting\ninterdot motion as the dominant mechanism for bichromatic driving.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermally activated intersubband scattering and oscillating\n  magnetoresistance in quantum wells: Experimental studies of magnetoresistance in high-mobility wide quantum wells\nreveal oscillations which appear with an increase in temperature to 10 K and\nwhose period is close to that of Shubnikov-de Haas oscillations. The observed\nphenomenon is identified as magnetointersubband oscillations caused by the\nscattering of electrons between two occupied subbands and the third subband\nwhich becomes occupied as a result of thermal activation. These small-period\noscillations are less sensitive to thermal suppression than the largeperiod\nmagnetointersubband oscillations caused by the scattering between the first and\nthe second subbands. Theoretical study, based on consideration of electron\nscattering near the edge of the third subband, gives a reasonable explanation\nof our experimental findings.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dirac-Harper Theory for One Dimensional Moir\u00e9 Superlattices: We study a Dirac Harper model for moir\\'e bilayer superlattices where layer\nantisymmetric strain periodically modulates the interlayer coupling between two\nhoneycomb lattices in one spatial dimension. Discrete and continuum\nformulations of this model are analyzed. For sufficiently long moir\\'e period\nthe we find low energy spectra that host a manifold of weakly dispersive bands\narising from a hierarchy of momentum and position dependent mass inversions. We\nanalyze their charge distributions, mode count and valley-coherence using exact\nsymmetries of the lattice model and approximate symmetries of a four-flavor\nversion of the Jackiw-Rebbi one dimensional solution.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Opto-Electronic Characterization of Three Dimensional Topological\n  Insulators: We demonstrate that the terahertz/infrared radiation induced photogalvanic\neffect, which is sensitive to the surface symmetry and scattering details, can\nbe applied to study the high frequency conductivity of the surface states in\n(Bi1-xSbx)2Te3 based three dimensional (3D) topological insulators (TI). In\nparticular, measuring the polarization dependence of the photogalvanic current\nand scanning with a micrometre sized beam spot across the sample, provides\naccess to (i) topographical inhomogeneity's in the electronic properties of the\nsurface states and (ii) the local domain orientation. An important advantage of\nthe proposed method is that it can be applied to study TIs at room temperature\nand even in materials with a high electron density of bulk carriers.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ground-state quantum geometry in superconductor-quantum dot chains: Multiterminal Josephson junctions constitute engineered topological systems\nin arbitrary synthetic dimensions defined by the superconducting phases.\nMicrowave spectroscopy enables the measurement of the quantum geometric tensor,\na fundamental quantity describing both the quantum geometry and the topology of\nthe emergent Andreev bound states in a unified manner. In this work we propose\nan experimentally feasible multiterminal setup of $N$ quantum dots connected to\n$N+1$ superconducting leads to study nontrivial topology in terms of the\nmany-body Chern number of the ground state. Moreover, we generalize the\nmicrowave spectroscopy scheme to the multiband case and show that the elements\nof the quantum geometric tensor of the noninteracting ground state can be\nexperimentally accessed from the measurable oscillator strengths at low\ntemperature.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hole Spin Coherence in a Ge/Si Heterostructure Nanowire: Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si\nnanowire double quantum dot using a fast pulsed-gate method and dispersive\nreadout. An inhomogeneous dephasing time $T_2^* \\sim 0.18~\\mathrm{\\mu s}$\nexceeds corresponding measurements in III-V semiconductors by more than an\norder of magnitude, as expected for predominately nuclear-spin-free materials.\nDephasing is observed to be exponential in time, indicating the presence of a\nbroadband noise source, rather than Gaussian, previously seen in systems with\nnuclear-spin-dominated dephasing.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Orbital Magnetism of Graphene Nanostructures: Bulk and Confinement\n  Effects: We consider the orbital magnetic properties of non-interacting charge\ncarriers in graphene-based nanostructures in the low-energy regime. The\nmagnetic response of such systems results both, frombulk contributions and from\nconfinement effects that can be particularly strong in ballistic quantum dots.\nFirst we provide a comprehensive study of the magnetic susceptibility $\\chi$ of\nbulk graphene in a magnetic field for the different regimes arising from the\nrelative magnitudes of the energy scales involved, i.e. temperature, Landau\nlevel spacing and chemical potential. We show that for finite temperature or\nchemical potential, $\\chi$ is not divergent although the diamagnetic\ncontribution $\\chi_{0}$ from the filled valance band exhibits the well-known\n$-B^{-1/2}$ dependence. We further derive oscillatory modulations of $\\chi$,\ncorresponding to de Haas-van Alphen oscillations of conventional\ntwo-dimensional electron gases. These oscillations can be large in graphene,\nthereby compensating the diamagnetic contribution $\\chi_{0}$ and yielding a net\nparamagnetic susceptibility for certain energy and magnetic field regimes.\nSecond, we predict and analyze corresponding strong, confinement-induced\nsusceptibility oscillations in graphene-based quantum dots with amplitudes\ndistincly exceeding the corresponding bulk susceptibility. Within a\nsemiclassical approach we derive generic expressions for orbital magnetism of\ngraphene quantum dots with regular classical dynamics. Graphene-specific\nfeatures can be traced back to pseudospin interference along the underlying\nperiodic orbits. We demonstrate the quality of the semiclassical approximation\nby comparison with quantum mechanical results for two exemplary mesoscopic\nsystems, a graphene disk with infinite mass-type edges and a rectangular\ngraphene structure with armchair and zigzag edges, using numerical\ntight-binding calculations in the latter case.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-orbit interactions mediated negative differential resistance in a\n  quasi-two-dimensional electron gas with finite thickness: Effects of the spin-orbit interactions on the energy spectrum, Fermi surface\nand spin dynamics are studied in structural- and bulk-inversion asymmetric\nquasi-two-dimensional structures with a finite thickness in the presence of a\nparabolic transverse confining potential. One-particle quantum mechanical\nproblem in the presence of an in-plane magnetic field is solved numerically\nexact. Interplay of the spin-orbit interactions, orbital- and Zeeman-effects of\nthe in-plane magnetic field yields a multi-valley subband structure, typical\nfor realization of the Gunn effect. A possible Gunn-effect-mediated spin\naccumulation is discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Modulation theory of quantum tunneling into a Calogero-Sutherland fluid: Quantum hydrodynamics of interacting electrons with a parabolic single\nparticle spectrum is studied using the Calogero-Sutherland model. The effective\naction and modulation equations, describing evolution of periodic excitations\nin the fluid, are derived. Applications to the problem of a single electron\ntunneling into the FQHE edge state are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Purcell effect at metal-insulator transitions: We investigate the spontaneous emission rate of a two-level quantum emitter\nnext to a composite medium made of randomly distributed metallic inclusions\nembedded in a dielectric host matrix. In the near-field, the Purcell factor can\nbe enhanced by two-orders of magnitude relative to the case of an homogeneous\nmetallic medium, and reaches its maximum precisely at the insulator-metal\ntransition. By unveiling the role of the decay pathways on the emitter's\nlifetime, we demonstrate that, close to the percolation threshold, the\nradiation emission process is dictated by electromagnetic absorption in the\nheterogeneous medium. We show that our findings are robust against change in\nmaterial properties, shape of inclusions, and apply for different effective\nmedium theories as well as for a wide range of transition frequencies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Correlated Insulator Behaviour at Half-Filling in Magic Angle Graphene\n  Superlattices: Van der Waals (vdW) heterostructures are an emergent class of metamaterials\ncomprised of vertically stacked two-dimensional (2D) building blocks, which\nprovide us with a vast tool set to engineer their properties on top of the\nalready rich tunability of 2D materials. One of the knobs, the twist angle\nbetween different layers, plays a crucial role in the ultimate electronic\nproperties of a vdW heterostructure and does not have a direct analog in other\nsystems such as MBE-grown semiconductor heterostructures. For small twist\nangles, the moir\\'e pattern produced by the lattice misorientation creates a\nlong-range modulation. So far, the study of the effect of twist angles in vdW\nheterostructures has been mostly concentrated in graphene/hexagonal boron\nnitride (h-BN) twisted structures, which exhibit relatively weak interlayer\ninteraction due to the presence of a large bandgap in h-BN. Here we show that\nwhen two graphene sheets are twisted by an angle close to the theoretically\npredicted 'magic angle', the resulting flat band structure near charge\nneutrality gives rise to a strongly-correlated electronic system. These flat\nbands exhibit half-filling insulating phases at zero magnetic field, which we\nshow to be a Mott-like insulator arising from electrons localized in the\nmoir\\'e superlattice. These unique properties of magic-angle twisted bilayer\ngraphene (TwBLG) open up a new playground for exotic many-body quantum phases\nin a 2D platform made of pure carbon and without magnetic field. The easy\naccessibility of the flat bands, the electrical tunability, and the bandwidth\ntunability though twist angle may pave the way towards more exotic correlated\nsystems, such as unconventional superconductors or quantum spin liquids.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Enhanced thermoelectric response in the fractional quantum Hall effect: We study the linear thermoelectric response of a quantum dot embedded in a\nconstriction of a quantum Hall bar with fractional filling factors nu=1/m\nwithin Laughlin series. We calculate the figure of merit ZT for the maximum\nefficiency at a fixed temperature difference. We find a significant enhancement\nof this quantity in the fractional filling in relation to the integer-filling\ncase, which is a direct consequence of the fractionalization of the electron in\nthe fractional quantum Hall state. We present simple theoretical expressions\nfor the Onsager coefficients at low temperatures, which explicitly show that ZT\nand the Seebeck coefficient increase with m.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin soliton of Holstein model with spin-orbit coupling in\n  one-dimensional conjugated polymers: For Holstein model with Rashba spin-orbit coupling (SOC) we establish the\nnonlinear Schr\\\"odinger equations and obtain exact soliton solution\nanalytically. It is found that the soliton is spin polarized determined both by\nthe SOC and the electron-phonon (e-ph) interaction. The soliton can be used to\ndescribe the spin transport or spin current in organic semiconductors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport signatures of symmetry protection in 1D Floquet topological\n  insulators: Time-periodic external drives have emerged as a powerful tool to artificially\ncreate topological phases of matter. Prime examples are Floquet topological\ninsulators (FTIs), where a gapped bulk supports in-gap edge states, protected\nagainst symmetry-preserving local perturbations. Similar to an ordinary static\ntopological insulator, the robustness of an edge state in a one-dimensional\n(1D) FTI shows up as a pinning of its quasienergy level, but now inside one of\ntwo distinct bulk gaps. Here we propose a scheme for probing this unique\nfeature by observing transport characteristics of a 1D finite-sized FTI\nattached to external leads. We present predictions for transmission spectra\nusing a nonequilibrium Green's function approach. Our analysis covers FTIs with\ntime-independent and periodically driven boundary perturbations which either\npreserve or break the protecting chiral symmetry.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effective Hamiltonians in the Quantum Rabi Problem: We revisit the theoretical description of the ultrastrong light-matter\ninteraction in terms of exactly solvable effective Hamiltonians. A perturbative\napproach based on polaronic and spin-dependent squeezing transformations\nprovides an effective Hamiltonian for the quantum Rabi model up to the second\norder in the expansion parameter. The model consistently includes both rotating\nand counter-rotating terms, going therefore beyond the rotating wave\napproximation. Analytical and numerical results show that the proposed\nHamiltonian performs better than the Bloch-Siegert model when calculating\noperator averages (e.g.\\, the mean photon number and number of excitations).\nThis improvement is due to a refined calculation of the dressed states within\nthe present model. Regarding the frequency shift induced by the qubit-photon\ninteraction, we find a different sign from the Bloch-Siegert value. This\ninfluences the eigenstates structure in a non-trivial way and ensures the\ncorrect calculation of the number of excitations associated to a given dressed\nstate. As a consistency check, we show that the exactly solvable independent\nboson model is reproduced as a special limit case of the perturbative\nHamiltonian.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "All-electron GW calculation for molecules: Ionization energy and\n  electron affinity of conjugated molecules: An efficient all-electron G$^0$W$^0$ method and a quasiparticle\nselfconsistent GW (QSGW) method for molecules are proposed in the molecular\norbital space with the full random phase approximation. The convergence with\nbasis set is examined. As an application, the ionization energy ($I$) and\nelectron affinity ($A$) of a series of conjugated molecules (up to 32 atoms)\nare calculated and compared to experiment. The QSGW result improves the\nG$^0$W$^0$ result and both of them are in significantly better agreement with\nexperimental data than those from Hartree-Fock (HF) and hybrid density\nfunctional calculations, especially for $A$. The nearly correct energy gap and\nsuppressed self-interaction error by the HF exchange make our method a good\ncandidate for investigating electronic and transport properties of molecular\nsystems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Through-membrane electron-beam lithography for ultrathin membrane\n  applications: We present a technique to fabricate ultrathin (down to 20 nm) uniform\nelectron transparent windows at dedicated locations in a SiN membrane for in\nsitu transmission electron microscopy experiments. An electron-beam (e-beam)\nresist is spray-coated on the backside of the membrane in a KOH- etched cavity\nin silicon which is patterned using through-membrane electron-beam lithography.\nThis is a controlled way to make transparent windows in membranes, whilst the\ntopside of the membrane remains undamaged and retains its flatness. Our\napproach was optimized for MEMS-based heating chips but can be applied to any\nchip design. We show two different applications of this technique for (1)\nfabrication of a nanogap electrode by means of electromigration in thin\nfree-standing metal films and (2) making low-noise graphene nanopore devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunable optical nonlinearity for TMD polaritons dressed by a Fermi sea: We study a system of a transition metal dichalcogenide (TMD) monolayer placed\nin an optical resonator, where strong light-matter coupling between excitons\nand photons is achieved. We present quantitative theory of the nonlinear\noptical response for exciton-polaritons for the case of doped TMD monolayer,\nand analyze in detail two sources of nonlinearity. The first nonlinear response\ncontribution stems from the Coulomb exchange interaction between excitons. The\nsecond contribution comes from the reduction of Rabi splitting that originates\nfrom phase space filling at increased exciton concentration and the composite\nnature of excitons. We demonstrate that both nonlinear contributions are\nenhanced in the presence of free electrons. As free electron concentration can\nbe routinely controlled by an externally applied gate voltage, this opens a way\nof electrical tuning of the nonlinear optical response.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "New Multi-Scale Simulation Framework for Next-Generation Electronic\n  Design Automation with Application to the Junctionless Transistor: In this paper we present a new multi-scale simulation scheme for\nnext-generation electronic design automation for nano-electronics. The scheme\nfeatures a combination of the first-principles quantum mechanical calculation,\nsemi-classical semiconductor device simulation, compact model generation and\ncircuit simulation. To demonstrate the feasibility of the proposed scheme, we\napply our newly developed quantum mechanics/electromagnetics method to simulate\nthe junctionless transistors. The simulation results are consistent with the\nexperimental measurements and provide new insights on the depletion effect of\nthe hetero-doped gate on the drain current. Based on the calculated I-V curves,\na compact model is then constructed for the junctionless transistors. The\nvalidity of the compact model is further verified by the transient circuit\nsimulation of an inverter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dual-gated hBN/bilayer-graphene superlattices and the transitions\n  between the insulating phases at the charge neutrality point: We report on transport properties in dual-gated hexagonal boron nitride\n(hBN)/bilayer-graphene (BLG) superlattices. Here, BLG is nontwisted, i.e.,\nplain. This paper focuses on the charge neutrality point (CNP) for a plain BLG.\nUnder a perpendicular magnetic field, transitions between two insulating phases\nat the CNP are detected by varying a displacement field with the study on the\nresistance-temperature characteristics and the magnetoresistance. This work\nopens avenues for exploring the global phase diagram of the hBN/BLG\nsuperlattices beyond the CNP.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Organic single-photon switch: The recent progress in nanotechnology [1,2] and single-molecule spectroscopy\n[3-5] paves the way for cost-effective organic quantum optical technologies\nemergent with a promise to real-life devices operating at ambient conditions.\nIn this letter, we harness $\\pi$-conjugated segments of an organic ladder-type\npolymer strongly coupled to a microcavity forming correlated collective dressed\nstates of light, so-called of exciton-polariton condensates. We explore an\nefficient way for all-optical ultra-fast control over the macroscopic\ncondensate wavefunction via a single photon. Obeying Bose statistics,\nexciton-polaritons exhibit an extreme nonlinearity undergoing bosonic\nstimulation [6] which we have managed to trigger at the single-photon level.\nRelying on the nature of organic matter to sustain stable excitons dressed with\nhigh energy molecular vibrations we have developed a principle that allows for\nsingle-photon nonlinearity operation at ambient conditions opening the door for\npractical implementations like sub-picosecond switching, amplification and\nall-optical logic at the fundamental limit of single light quanta.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical nanoscopy via quantum control: We present a scheme for nanoscopic imaging of a quantum mechanical two-level\nsystem using an optical probe in the far-field. Existing super-resolution\nschemes require more than two-levels and depend on an incoherent response to\nthe lasers. Here, quantum control of the two states proceeds via rapid\nadiabatic passage. We implement this scheme on an array of semiconductor\nself-assembled quantum dots. Each quantum dot results in a bright spot in the\nimage with extents down to 30 nm ({\\lambda}/31). Rapid adiabatic passage is\nestablished as a versatile tool in the super-resolution toolbox.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strain-induced pseudomagnetic and scalar fields in symmetry-enforced\n  Dirac nodes: It is known that Dirac nodes can be present at high-symmetry points of\nBrillouin zone only for certain space groups. For these cases, the effect of\nstrain is treated by symmetry considerations. The dependence of strain-induced\npotentials on the strain tensor is found. In all but two cases, the\npseudomagnetic field potential is present. It can be used to control valley\ncurrents.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Chargeless spin current for switching and coupling of domain walls in\n  magnetic nanowires: The demonstration of the generation and control of a pure spin current\n(without net charge flow) by electric fields and/or temperature gradient has\nbeen an essential leap in the quest for low-power consumption electronics. The\nkey issue of whether and how such a current can be utilized to drive and\ncontrol information stored in magnetic domain walls (DWs) is still outstanding\nand is addressed here. We demonstrate that pure spin current acts on DWs in a\nmagnetic stripe with an effective spin-transfer torque resulting in a mutual\nDWs separation dynamics and picosecond magnetization reversal. In addition,\nlong-range ($\\sim$ mm) antiferromagnetic DWs coupling emerges. If one DW is\npinned by geometric constriction, the spin current induces a dynamical spin\norbital interaction that triggers an internal electric field determined by\n$\\vec{E} \\sim \\hat{e}_{x} \\cdot (\\vec{n}_{1} \\times \\vec{n}_{2})$ where\n$\\vec{n}_{1/2}$ are the effective DWs orientations and $\\hat{e}_{x} $ is their\nspatial separation vector. This leads to charge accumulation or persistent\nelectric current in the wire. As DWs are routinely realizable and tuneable, the\npredicted effects bear genuine potential for power-saving spintronics devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Single-Particle-Picture Breakdown in laterally weakly confining GaAs\n  Quantum Dots: We present a detailed investigation of different excitonic states weakly\nconfined in single GaAs/AlGaAs quantum dots obtained by the Al droplet-etching\nmethod. For our analysis we make use of temperature-, polarization- and\nmagnetic field-dependent $\\mu$-photoluminescence measurements, which allow us\nto identify different excited states of the quantum dot system. Besides that,\nwe present a comprehensive analysis of g-factors and diamagnetic coefficients\nof charged and neutral excitonic states in Voigt and Faraday configuration.\nSupported by theoretical calculations by the Configuration interaction method,\nwe show that the widely used single-particle Zeeman Hamiltonian cannot be used\nto extract reliable values of the g-factors of the constituent particles from\nexcitonic transition measurements.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic Structure of Nano-Graphite Moebius Ribbon: We consider the electronic and magnetic properties of nanographite ribbon\nwith zigzag edges under the periodic or Moebius boundary conditions. The zigzag\nnano-graphite ribbons possess edge localized states at the Fermi level which\ncause a ferrimagnetic spin polarization localized at the edge sites even in the\nvery weak Coulomb interaction. The imposition of the Moebius boundary condition\nmakes the system non-AB-bipartite lattice, and depress the spin polarization,\nresulting in the formation of a magnetic domain wall. The width of the magnetic\ndomain depends on the Coulomb interaction and narrows with increasing U/t.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Valley-Polarized Quantum Anomalous Hall State in Moir\u00e9\n  MoTe$_2$/WSe$_2$ Heterobilayers: Moir\\'e heterobilayer transition metal dichalcogenides (TMDs) emerge as an\nideal system for simulating the single-band Hubbard model and interesting\ncorrelated phases have been observed in these systems. Nevertheless, the\nmoir\\'e bands in heterobilayer TMDs were believed to be topologically trivial.\nRecently, it was reported that both a quantum valley Hall insulating state at\nfilling $\\nu=2$ (two holes per moir\\'e unit cell) and a valley-polarized\nquantum anomalous Hall state at filling $\\nu=1$ were observed in AB stacked\nmoir\\'e MoTe$_2$/WSe$_2$ heterobilayers. However, how the topologically\nnontrivial states emerge is not known. In this work, we propose that the\npseudo-magnetic fields induced by lattice relaxation in moir\\'e\nMoTe$_2$/WSe$_2$ heterobilayers could naturally give rise to moir\\'e bands with\nfinite Chern numbers. We show that a time-reversal invariant quantum valley\nHall insulator is formed at full-filing $\\nu=2$, when two moir\\'e bands with\nopposite Chern numbers are filled. At half-filling $\\nu=1$, Coulomb interaction\nlifts the valley degeneracy and results in a valley-polarized quantum anomalous\nHall state, as observed in the experiment. Our theory identifies a new way to\nachieve topologically non-trivial states in heterobilayer TMD materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Theoretical Description of Scanning Tunneling Potentiometry: A theoretical description of scanning tunneling potentoimetry (STP)\nmeasurement is presented to address the increasing need for a basis to\ninterpret experiments on macrscopic samples. Based on a heuristic understanding\nof STP provided to facilitate theoretical understanding, the total tunneling\ncurrent related to the density matrix of the sample is derived within the\ngeneral framework of quantum transport. The measured potentiometric voltage is\ndetermined implicitly as the voltage necessary to null the tunneling current.\nExplicit expressions of measured voltages are presented under certain\nassumptions, and limiting cases are discussed to connect to previous results.\nThe need to go forward and formulate the theory in terms of a local density\nmatrix is also discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anisotropic thermoelectric effect in helimagnetic tunnel junctions: Thermoelectric transport across\nnormal-metal/helical-multiferroic/ferromagnetic heterojunctions is\ntheoretically investigated. We find a anisotropic charge and spin thermopower\nwith a $C_{2v}$ symmetry. The angular dependence on the magnetization\norientation of the ferromagnetic layer is substantiated by a phenomenological\ntheory based on the symmetry of the effective spin-orbit interaction induced by\nthe topology of the spiral magnetic order in the multiferroic barrier.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetoresistance in the in-plane magnetic field induced semi-metallic\n  phase of inverted HgTe quantum wells: In this study we have measured the magnetoresistance response of inverted\nHgTe quantum wells in the presence of a large parallel magnetic field up to 33\nT is applied. We show that in quantum wells with inverted band structure a\nmonotonically decreasing magnetoresistance is observed when a magnetic field up\nto order 10 T is applied parallel to the quantum well plane. This feature is\naccompanied by a vanishing of non-locality and is consistent with a predicted\nmodification of the energy spectrum that becomes gapless at a critical in-plane\nfield $B_{c}$. Magnetic fields in excess of $B_c$ allow us to investigate the\nevolution of the magnetoresistance in this field-induced semi-metallic region\nbeyond the known regime. After an initial saturation phase in the presumably\ngapless phase, we observe a strong upturn of the longitudinal resistance. A\nsmall residual Hall signal picked up in non-local measurements suggests that\nthis feature is likely a bulk phenomenon and caused by the semi-metallicity of\nthe sample. Theoretical calculations indeed support that the origin of these\nfeatures is classical and a power law upturn of the resistance can be expected\ndue to the specifics of two-carrier transport in thin (semi-)metallic samples\nsubjected to large magnetic fields.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic structure of graphene on single crystal copper substrates: The electronic structure of graphene on Cu(111) and Cu(100) single crystals\nis investigated using low energy electron microscopy, low energy electron\ndiffraction and angle resolved photoemission spectroscopy. On both substrates\nthe graphene is rotationally disordered and interactions between the graphene\nand substrate lead to a shift in the Dirac crossing of $\\sim$ -0.3 eV and the\nopening of a $\\sim$ 250 meV gap. Exposure of the samples to air resulted in\nintercalation of oxygen under the graphene on Cu(100), which formed a\n($\\sqrt{2} \\times 2\\sqrt{2}$)R45$^{\\rm o}$ superstructure. The effect of this\nintercalation on the graphene $\\pi$ bands is to increase the offset of the\nDirac crossing ($\\sim$ -0.6 eV) and enlarge the gap ($\\sim$ 350 meV). No such\neffect is observed for the graphene on Cu(111) sample, with the surface state\nat $\\Gamma$ not showing the gap associated with a surface superstructure. The\ngraphene film is found to protect the surface state from air exposure, with no\nchange in the effective mass observed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Semiclassical Theory for Decay and Fragmentation Processes in Chaotic\n  Quantum Systems: We consider quantum decay and photofragmentation processes in open chaotic\nsystems in the semiclassical limit. We devise a semiclassical approach which\nallows us to consistently calculate quantum corrections to the classical decay\nto high order in an expansion in the inverse Heisenberg time. We present\nresults for systems with and without time reversal symmetry and also for the\nsymplectic case, as well as extending recent results to non-localized initial\nstates. We further analyze related photodissociation and photoionization\nphenomena and semiclassically compute cross-section correlations, including\ntheir Ehrenfest time dependence.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Midinfrared Third Harmonic Generation from Macroscopically Aligned\n  Ultralong Single-Wall Carbon Nanotubes: We report the observation of strong third harmonic generation from a\nmacroscopic array of aligned ultralong single-wall carbon nanotubes (SWCNTs)\nwith intense midinfrared radiation. Through power-dependent experiments, we\ndetermined the absolute value of the third-order nonlinear optical\nsusceptibility, $\\chi^{(3)}$, of our SWCNT film to be 5.53 $\\times$ 10$^{-12}$\nesu, three orders of magnitude larger than that of the fused silica reference\nwe used. Taking account of the filling factor of 8.75% for our SWCNT film, we\nestimate a $\\chi^{(3)}$ of 6.32 $\\times$ 10$^{-11}$ esu for a fully dense film.\nFurthermore, through polarization-dependent experiments, we extracted all the\nnonzero elements of the $\\chi^{(3)}$ tensor, determining the magnitude of the\nweaker tensor elements to be $\\sim$1/6 of that of the dominant\n$\\chi^{(3)}_{zzzz}$ component.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Do the Size Effects Exist?: In this short paper we review a series of publications, some of which are our\nown, where various aspects of size effects were examined. By analyzing a series\nof examples we show that various intensive macroscopic characteristics of\nnanoobjects exhibit non-trivial size dependencies on the scale of 200 to 40 A.\nDrastic variations take place for sizes in the region 50-60 A for ordinary\nsystems, and 60-200 A in the case of magnetic systems. We argue that X-ray and\nneutron scattering gives an excellent metrological support in the domain from\n100 A to 10 A.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Superconductor-semiconductor magnetic microswitch: A hybrid superconductor--two-dimensional electron gas microdevice is\npresented. Its working principle is based on the suppression of Andreev\nreflection at the superconductor-semiconductor interface caused by a magnetic\nbarrier generated by a ferromagnetic strip placed on top of the structure.\nDevice switching is predicted with fields up to some mT and working frequencies\nof several GHz, making it promising for applications ranging from microswitches\nand storage cells to magnetic field discriminators.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Influence of vibrational modes on the electronic properties of DNA: We investigate the electron (hole) transport through short double-stranded\nDNA wires in which the electrons are strongly coupled to the specific\nvibrational modes (vibrons) of the DNA. We analyze the problem starting from a\ntight-binding model of DNA, with parameters derived from ab-initio\ncalculations, and describe the dissipative transport by equation-of-motion\ntechniques. For homogeneous DNA sequences like Poly- (Guanine-Cytosine) we find\nthe transport to be quasi-ballistic with an effective density of states which\nis modified by the electron-vibron coupling. At low temperatures the linear\nconductance is strongly enhanced, but above the `semiconducting' gap it is\naffected much less. In contrast, for inhomogeneous (`natural') sequences almost\nall states are strongly localized, and transport is dominated by dissipative\nprocesses. In this case, a non-local electron-vibron coupling influences the\nconductance in a qualitative and sequence-dependent way.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Giant Microwave Sensitivity of Magnetic Array by Long-Range Chiral\n  Interaction Driven Skin Effect: Non-Hermitian skin effect was observed in one-dimensional systems with\nshort-range chiral interaction. Long-range chiral interaction mediated by\ntraveling waves also favors the accumulation of energy, but has not yet showed\nnon-Hermitian topology. Here we find that the strong interference brought by\nthe wave propagation is detrimental for accumulation. By suppression of\ninterference via the damping of traveling waves, we predict the non-Hermitian\nskin effect of magnetic excitation in a periodic array of magnetic nanowires\nthat are coupled chirally via spin waves of thin magnetic films. The local\nexcitation of a wire at one edge by weak microwaves of magnitude $\\sim \\mu{\\rm\nT}$ leads to a considerable spin-wave amplitude at the other edge, i.e. a\nremarkable functionality useful for sensitive, non-local, and non-reciprocal\ndetection of microwaves.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Generating indistinguishable photons from a quantum dot in a noisy\n  environment: Single photons from semiconductor quantum dots are promising resources for\nlinear optical quantum computing, or, when coupled to spin states, quantum\nrepeaters. To realize such schemes, the photons must exhibit a high degree of\nindistinguishability. However, the solid-state environment presents inherent\nobstacles for this requirement as intrinsic semiconductor fluctuations can\ndestroy the photon indistinguishability. Here we use resonance fluorescence to\ngenerate indistinguishable photons from a single quantum dot in an environment\nfilled with many charge-fluctuating traps. Over long time-scales ($>50$\n$\\mu$s), flickering of the emission due to significant spectral fluctuations\nreduce the count rates. Nevertheless, due to the specificity of resonance\nfluorescence, high-visibility two-photon interference is achieved.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cavity optomechanical transduction sensing of single molecules: We report narrow linewidth optomechanical oscillation of a silica microsphere\nimmersed in a buffer solution. Through a novel optomechanical transduction\nsensing approach, single 10-nm-radius silica beads and Bovine serum albumin\n(BSA) protein molecules with a molecular weight of 66 kDalton were detected.\nThis approach predicts the detection of 3.9 kDalton single molecules at a\nsignal-to-noise ration above unity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-Hermitian Lindhard function and Friedel oscillations: The Lindhard function represents the basic building block of many-body\nphysics and accounts for charge response, plasmons, screening, Friedel\noscillation, RKKY interaction etc. Here we study its non-Hermitian version in\none dimension, where quantum effects are traditionally enhanced due to spatial\nconfinement, and analyze its behavior in various limits of interest. Most\nimportantly, we find that the static limit of the non-Hermitian Lindhard\nfunction has no divergence at twice the Fermi wavenumber and vanishes\nidentically for all other wavenumbers at zero temperature. Consequently, no\nFriedel oscillations are induced by a non-Hermitian, imaginary impurity to\nlowest order in the impurity potential at zero temperature. Our findings are\ncorroborated numerically on a tight-binding ring by switching on a weak real or\nimaginary potential. We identify conventional Friedel oscillations or heavily\nsuppressed density response, respectively.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The effects of a magnetic barrier and a nonmagnetic spacer in tunnel\n  structures: The spin-polarized transport is investigated in a new type of magnetic tunnel\njunction which consists of two ferromagnetic electrodes separated by a magnetic\nbarrier and a nonmagnetic metallic spacer. Based on the transfer matrix method\nand the nearly-free-electron-approximation the dependence of the tunnel\nmagnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer\nthickness and the applied bias voltage are studied theoretically. The TMR and\nspin polarization show an oscillatory behavior as a function of the spacer\nthickness and the bias voltage. The oscillations originate from the quantum\nwell states in the spacer, while the existence of the magnetic barrier gives\nrise to a strong spin polarization and high values of the TMR. Our results may\nbe useful for the development of spin electronic devices based on coherent\ntransport.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mode- and size-dependent Landau-Lifshitz damping in magnetic\n  nanostructures: Evidence for non-local damping: We demonstrate a strong dependence of the effective damping on the nanomagnet\nsize and the particular spin-wave mode that can be explained by the theory of\nintralayer transverse-spin-pumping. The effective Landau-Lifshitz damping is\nmeasured optically in individual, isolated nanomagnets as small as 100 nm. The\nmeasurements are accomplished by use of a novel heterodyne magneto-optical\nmicrowave microscope with unprecedented sensitivity. Experimental data reveal\nmultiple standing spin-wave modes that we identify by use of micromagnetic\nmodeling as having either localized or delocalized character, described\ngenerically as end- and center-modes. The damping parameter of the two modes\ndepends on both the size of the nanomagnet as well as the particular spin-wave\nmode that is excited, with values that are enhanced by as much as 40% relative\nto that measured for an extended film. Contrary to expectations based on the ad\nhoc consideration of lithography-induced edge damage, the damping for the\nend-mode decreases as the size of the nanomagnet decreases. The data agree with\nthe theory for damping caused by the flow of intralayer transverse\nspin-currents driven by the magnetization curvature. These results have serious\nimplications for the performance of nanoscale spintronic devices such as\nspin-torque-transfer magnetic random access memory.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Resistivity of Graphene Nanoribbon Interconnects: Graphene nanoribbon interconnects are fabricated, and the extracted\nresistivity is compared to that of Cu. It is found that the average resistivity\nat a given line-width (18nm<W<52nm) is about 3X that of a Cu wire, whereas the\nbest GNR has a resistivity comparable to that of Cu. The conductivity is found\nto be limited by impurity scattering as well as LER scattering; as a result,\nthe best reported GNR resistivity is 3X the limit imposed by substrate phonon\nscattering. This study reveals that even moderate-quality graphene nanowires\nhave the potential to outperform Cu for use as on-chip interconnects.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Resistivity anisotropy of quantum Hall stripe phases: Quantum Hall stripe phases near half-integer filling factors $\\nu \\ge 9/2$\nwere predicted by Hartree-Fock (HF) theory and confirmed by discoveries of\ngiant resistance anisotropies in high-mobility two-dimensional electron gases.\nA theory of such anisotropy was proposed by MacDonald and Fisher, although they\nused parameters whose dependencies on the filling factor, electron density, and\nmobility remained unspecified. Here, we fill this void by calculating the\nhard-to-easy resistivity ratio as a function of these three variables.\nQuantitative comparison with experiment yields very good agreement which we\nview as evidence for the \"plain vanilla\" smectic stripe HF phases.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dephasing of a particle in a dissipative environment: The motion of a particle in a ring of length L is influenced by a dirty metal\nenvironment whose fluctuations are characterized by a short correlation\ndistance $\\ell << L$. We analyze the induced decoherence process, and compare\nthe results with those obtained in the opposing Caldeira-Leggett limit ($\\ell\n>> L$). A proper definition of the dephasing factor that does not depend on a\nvague semiclassical picture is employed. Some recent Monte-Carlo results about\nthe effect of finite temperatures on \"mass renormalization\" in this system are\nilluminated.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Intercalated Rare-Earth Metals under Graphene on SiC: Intercalation of rare earth metals ($RE$ = Eu, Dy, and Gd) is achieved by\ndepositing the $RE$ metal on graphene that is grown on silicon-carbide (SiC)\nand by subsequent annealing at high temperatures to promote intercalation. STM\nimages of the films reveal that the graphene layer is defect free and that each\nof the intercalated metals has a distinct nucleation pattern. Intercalated Eu\nforms nano-clusters that are situated on the vertices of a Moir{\\`e} pattern,\nwhile Dy and Gd form randomly distributed nano-clusters. X-ray magnetic\ncircular dichroism (XMCD) measurements of intercalated films reveal the\nmagnetic properties of these $RE$'s nano-clusters. Furthermore, field\ndependence and temperature dependence of the magnetic moments extracted from\nthe XMCD show paramagnetic-like behaviors with moments that are generally\nsmaller than those predicted by the Brillouin function. XMCD measurements of\n$RE$-oxides compared with those of the intercalated $RE$'s under graphene after\nexposure to air for months indicate that the graphene membranes protect these\nintercalants against oxidation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hot carriers in a bipolar graphene: Hot carriers in a doped graphene under dc electric field is described taking\ninto account the intraband energy relaxation due to acoustic phonon scattering\nand the interband generation-recombination transitions caused by thermal\nradiation. The consideration is performed for the case when the intercarrier\nscattering effectively establishes the quasiequilibrium electron-hole\ndistributions, with effective temperature and concentrations of carriers. The\nconcentration and energy balance equations are solved taking into account an\ninterplay between weak energy relaxation and generation-recombination\nprocesses. The nonlinear conductivity is calculated for the momentum relaxation\ncaused by the elastic scattering. The current-voltage characteristics, and the\ntransition between bipolar and monopolar regimes of conductivity are obtained\nand analyzed, for different temperatures and gate voltages.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic-Field-Dependent Thermodynamic Properties of Square and\n  Quadrupolar Artificial Spin Ice: Applied magnetic fields are an important tuning parameter for artificial spin\nice (ASI) systems, as they can drive phase transitions between different\nmagnetic ground states, or tune through regimes with high populations of\nemergent magnetic excitations (e.g., monopole-like quasiparticles). Here, using\nsimulations supported by experiments, we investigate the thermodynamic\nproperties and magnetic phases of square and quadrupolar ASI as a function of\napplied in-plane magnetic fields. Monte Carlo simulations are used to generate\nfield-dependent maps of the magnetization, the magnetic specific heat, the\nthermodynamic magnetization fluctuations, and the magnetic order parameters,\nall under equilibrium conditions. These maps reveal the diversity of magnetic\norderings and the phase transitions that occur in different regions of the\nphase diagrams of these ASIs, and are experimentally supported by\nmagneto-optical measurements of the equilibrium \"magnetization noise\" in\nthermally-active ASIs.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effective interfacial Dzyaloshinskii-Moriya interaction and skyrmion\n  stabilization in ferromagnet/paramagnet and ferromagnet/superconductor hybrid\n  systems: It is shown that a term in the form of Dzyaloshinskii-Moriya interaction\n(DMI) contributes to the free energy of a ferromagnetic (FM) film on a\nparamagnetic (PM) (an FM above the critical temperature, Tc) or superconducting\n(SC) substrate occurring in the London limit. This contribution results from\nmagnetostatic interaction between the film and substrate under which the\nsubstrate affects FM magnetization back via its magnetic field produced by\nmagnetization inhomogeneity in the film. Strikingly, in the FM/PM system this\neffective DMI stabilizes chiral magnetic textures, e.g., magnetic skyrmions\n(MSk's) of the Neel-type, which is in contrast to that in the FM/SC one. A\nstrong temperature sensitivity of the effective DMI allows for tuning the\ncoupling between the FM film and PM or SC substrate and thus controlling the\nMSk radius in FM/PM.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A Movable Valley Switch Driven by Berry Phase in Bilayer Graphene\n  Resonators: Since its discovery, Berry phase has been demonstrated to play an important\nrole in many quantum systems. In gapped Bernal bilayer graphene, the Berry\nphase can be continuously tuned from zero to 2pi, which offers a unique\nopportunity to explore the tunable Berry phase on the physical phenomena. Here,\nwe report experimental observation of Berry phases-induced valley splitting and\ncrossing in moveable bilayer graphene p-n junction resonators. In our\nexperiment, the bilayer graphene resonators are generated by combining the\nelectric field of scanning tunneling microscope tip with the gap of bilayer\ngraphene. A perpendicular magnetic field changes the Berry phase of the\nconfined bound states in the resonators from zero to 2pi continuously and leads\nto the Berry phase difference for the two inequivalent valleys in the bilayer\ngraphene. As a consequence, we observe giant valley splitting and unusual\nvalley crossing of the lowest bound states. Our results indicate that the\nbilayer graphene resonators can be used to manipulate the valley degree of\nfreedom in valleytronics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Theory of the plasma-wave photoresponse of a gated graphene sheet: The photoresponse of graphene has recently received considerable attention.\nThe main mechanisms yielding a finite dc response to an oscillating radiation\nfield which have been investigated include responses of photovoltaic,\nphoto-thermoelectric, and bolometric origin. In this Article we present a fully\nanalytical theory of a photoresponse mechanism which is based on the excitation\nof plasma waves in a gated graphene sheet. By employing the theory of\nrelativistic hydrodynamics, we demonstrate that plasma-wave photodetection is\nsubstantially influenced by the massless Dirac fermion character of carriers in\ngraphene and that the efficiency of photodetection can be improved with respect\nto that of ordinary parabolic-band electron fluids in semiconductor\nheterostructures.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Active feedback of a Fabry-Perot cavity to the emission of a single\n  InAs/GaAs quantum dot: We present a detailed study of the use of Fabry-Perot (FP) cavities for the\nspectroscopy of single InAs quantum dots (QDs). We derive optimal cavity\ncharacteristics and resolution limits, and measure photoluminescence linewidths\nas low as 0.9 GHz. By embedding the QDs in a planar cavity, we obtain a\nsufficiently large signal to actively feed back on the length of the FP to lock\nto the emission of a single QD with a stability below 2% of the QD linewidth.\nAn integration time of approximately two seconds is found to yield an optimum\ncompromise between shot noise and cavity length fluctuations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fermionic and bosonic ac conductivities at strong disorder: We study the ac conduction in a system of fermions or bosons strongly\nlocalised in a disordered array of sites with short-range interactions at\nfrequencies larger than the intersite tunnelling but smaller than the\ncharacteristic fluctuation of the on-site energy. While the main contribution\n$\\sigma_0(\\omega)$ to the conductivity comes from local dipole-type excitations\non close pairs of sites, coherent processes on three or more sites lead to an\ninterference correction $\\sigma_1(\\omega)$, which depends on the statistics of\nthe charge carriers and can be suppressed by magnetic field. For bosons the\ncorrection is always positive, while for fermions it can be positive or\nnegative depending on whether the conduction is dominated by effective\nsingle-particle or single-hole processes. We calculate the conductivity\nexplicitly assuming a constant density of states of single-site excitations.\nIndependently of the statistics, $\\sigma_0(\\omega)=const$. For bosons\n$\\sigma_1(\\omega)\\propto \\log(C/\\omega)$. For fermions\n$\\sigma_1(\\omega)\\propto\\log[\\max(A,\\omega)/\\omega]-\\log[\\max(B,\\omega)/\\omega]$,\nwhere the first and the second term are respectively the particle and hole\ncontributions, $A$ and $B$ being the particle and hole energy cutoffs. The ac\nmagnetoresistance has the same sign as $\\sigma_1(\\omega)$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Absence of nonlocal resistance in microstructures of PbTe quantum wells: We report on experiments allowing to set an upper limit on the magnitude of\nthe spin Hall effect and the conductance by edge channels in quantum wells of\nPbTe embedded between PbEuTe barriers. We reexamine previous data obtained for\nepitaxial microstructures of n-type PbSe and PbTe, in which pronounced nonlocal\neffects and reproducible magnetoresistance oscillations were found. Here we\nshow that these effects are brought about by a quasi-periodic network of\nthreading dislocations adjacent to the BaF$_2$ substrate, which give rise to a\np-type interfacial layer and an associated parasitic parallel conductance. We\nthen present results of transport measurements on microstructures of modulation\ndoped PbTe/(Pb,Eu)Te:Bi heterostructures for which the influence of parasitic\nparallel conductance is minimized, and for which quantum Hall transport had\nbeen observed, on similar samples, previously. These structures are of H-shaped\ngeometry and they are patterned of 12 nm thick strained PbTe quantum wells\nembedded between Pb$_{0.92}$Eu$_{0.08}$Te barriers. The structures have\ndifferent lateral sizes corresponding to both diffusive and ballistic electron\ntransport in non-equivalent L valleys. For these structures no nonlocal\nresistance is detected confirming that PbTe is a trivial insulator. The\nmagnitude of spin Hall angle gamma is estimated to be smaller than 0.02 for\nPbTe/PbEuTe microstructures in the diffusive regime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Extraction of many-body configurations from nonlinear absorption in\n  semiconductor quantum wells: Detailed electronic many-body configurations are extracted from\nquantitatively measured timeresolved nonlinear absorption spectra of resonantly\nexcited GaAs quantum wells. The microscopic theory assigns the observed\nspectral changes to a unique mixture of electron-hole plasma, exciton, and\npolarization effects. Strong transient gain is observed only under co-circular\npump-probe conditions and is attributed to the transfer of pump-induced\ncoherences to the probe.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Long-time coherence in fourth-order spin correlation functions: We study the long-time decay of fourth-order electron spin correlation\nfunctions for an isolated singly charged semi-conductor quantum dot. The\nelectron spin dynamics is governed by the applied external magnetic field as\nwell as the hyperfine interaction. While the long-time coherent oscillations in\nthe correlation functions can be understood within an semi-classical approach\ntreating the Overhauser field as frozen, the field dependent decay of its\namplitude reported in different experiments cannot be explained by the\ncentral-spin model indicating the insufficiency of such a description. By\nincorporating the nuclear Zeeman splitting and the strain induced\nnuclear-electric quadrupolar interaction, we find the correct crossover from a\nfast decay in small magnetic fields to a slow exponential asymptotic in large\nmagnetic fields. It originates from a competition between the quadrupolar\ninteraction inducing an enhanced spin decay and the nuclear Zeeman term that\nsuppressed the spin-flip processes. We are able to explain the magnetic field\ndependency of the characteristic long-time decay time $T_2$ depending on the\nexperimental setups. The calculated asymptotic values of $T_2 = 3 -4\\,\\mu$s\nagree qualitatively well with the experimental data.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Wide range electrical tunability of single photon emission from\n  chromium-based colour centres in diamond: We demonstrate electrical control of the single photon emission spectrum from\nchromium-based colour centres implanted in monolithic diamond. Under an\nexternal electric field the tunability range is typically three orders of\nmagnitude larger than the radiative linewidth and at least one order of\nmagnitude larger than the observed linewidth. The electric and magnetic field\ndependence of luminescence gives indications on the inherent symmetry and we\npropose Cr-X or X-Cr-Y type noncentrosymmetric atomic configurations as most\nprobable candidates for these centres.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic Transport and Thermopower in 2D and 3D Heterostructures--A\n  Theory Perspective: In this review, we discuss the impact of interfaces and heterojuctions on the\nelectronic and thermoelectric transport properties of materials. We review\nrecent progress in understanding electronic transport in two-dimensional (2D)\nmaterials ranging from graphene to transition metal dichalcogenides (TMDs),\ntheir homojunctions (grain boundaries), lateral heterojunctions (such as\ngraphene/MoS$_2$ lateral interfaces), and vertical van der Waals (vdW)\nheterostructures. We also review work in thermoelectric properties of 2D\nheterojunctions, as well as their applications in creating devices such as\nresonant tunneling diodes (RTDs). Lastly, we turn our focus to work in\nthree-dimensional (3D) heterostructures. While transport in 3D heterostructures\nhas been researched for several decades, here we review recent progress in\ntheory and simulation of quantum effects on transport via the Wigner and\nnon-equilibrium Green's functions (NEGF) approaches. These simulation\ntechniques have been successfully applied toward understanding the impact of\nheterojunctions on the thermoelectric properties, with applications in energy\nharvesting, and electron resonant tunneling, with applications in RTDs. We\nconclude that tremendous progress has been made in both simulation and\nexperiments toward the goal of understanding transport in heterostructures and\nthis progress will soon be parlayed into improved energy converters and quantum\nnanoelectronic devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Stretching graphene using polymeric micro-muscles: The control of strain in two-dimensional materials opens exciting\nperspectives for the engineering of their electronic properties. While this\nexpectation has been validated by artificial-lattice studies, it remains\nelusive in the case of atomic lattices. Remarkable results were obtained on\nnanobubbles and nano-wrinkles, or using scanning probes; microscale strain\ndevices were implemented exploiting deformable substrates or external loads.\nThese devices lack, however, the flexibility required to fully control and\ninvestigate arbitrary strain profiles. Here, we demonstrate a novel approach\nmaking it possible to induce strain in graphene using polymeric micrometric\nartificial muscles (MAMs) that contract in a controllable and reversible way\nunder an electronic stimulus. Our method exploits the mechanical response of\npoly-methyl-methacrylate (PMMA) to electron-beam irradiation. Inhomogeneous\nanisotropic strain and out-of-plane deformation are demonstrated and studied by\nRaman, scanning-electron and atomic-force microscopy. These can all be easily\ncombined with the present device architecture. The flexibility of the present\nmethod opens new opportunities for the investigation of strain and\nnanomechanics in two-dimensional materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electrical and thermal transport through $\u03b1-T_3$ NIS junction: We investigate the electrical and thermal transport properties of the\n$\\alpha-T_3$ based normal metal-insulator-superconductor (NIS) junction using\nBlonder-Tinkham-Klapwijk (BTK) theory. We show that the tunneling conductance\nof the NIS junction is an oscillatory function of the effective barrier\npotential ($\\chi$) of the insulating region upto a thin barrier limit. The\nperiodicity and the amplitudes of the oscillations largely depend on the values\nof $\\alpha$ and the gate voltage of the superconducting region, namely, $U_0$.\nFurther, the periodicity of the oscillation changes from $\\pi$ to $\\pi/2$ as we\nincrease $U_0$. To assess the thermoelectric performance of such a junction, we\nhave computed the Seebeck coefficient, the thermoelectric figure of merit,\nmaximum power output, efficiency at the maximum output power of the system, and\nthe thermoelectric cooling of the NIS junction as a self-cooling device. Our\nresults on the thermoelectric cooling indicate practical realizability and\nusefulness for using our system as efficient cooling detectors, sensors, etc.,\nand hence could be crucial to the experimental success of the thermoelectric\napplications of such junction devices. Furthermore, for an $\\alpha-T_3$\nlattice, whose limiting cases denote a graphene or a dice lattice, it is\ninteresting to ascertain which one is more suitable as a thermoelectric device\nand the answer seems to depend on the $U_0$. We observe that for an\n$\\alpha-T_3$ lattice corresponding to $U_0=0$, graphene ($\\alpha=0$) is more\nfeasible for constructing a thermoelectric device, whereas for $U_0 \\gg E_F$,\nthe dice lattice ($\\alpha=1$) has a larger utility.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ab initio theory of electron-phonon mediated ultrafast spin relaxation\n  of laser-excited hot electrons in transition-metal ferromagnets: We report a computational theoretical investigation of electron spin-flip\nscattering induced by the electron-phonon interaction in the transition-metal\nferromagnets bcc Fe, fcc Co and fcc Ni. The Elliott-Yafet electron-phonon\nspin-flip scattering is computed from first-principles, employing a generalized\nspin-flip Eliashberg function as well as ab initio computed phonon dispersions.\nAiming at investigating the amount of electron-phonon mediated demagnetization\nin femtosecond laser-excited ferromagnets, the formalism is extended to treat\nlaser-created thermalized as well as nonequilibrium, nonthermal hot electron\ndistributions. Using the developed formalism we compute the phonon-induced spin\nlifetimes of hot electrons in Fe, Co, and Ni. The electron-phonon mediated\ndemagnetization rate is evaluated for laser-created thermalized and\nnonequilibrium electron distributions. Nonthermal distributions are found to\nlead to a stronger demagnetization rate than hot, thermalized distributions,\nyet their demagnetizing effect is not enough to explain the experimentally\nobserved demagnetization occurring in the subpicosecond regime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermoelectric and Seebeck coefficients of granular metals: In this work we present a detailed study and derivation of the thermopower\nand thermoelectric coefficient of nano-granular metals at large tunneling\nconductance between the grains, g_T>> 1. An important criterion for the\nperformance of a thermoelectric device is the thermodynamic figure of merit\nwhich is derived using the kinetic coefficients of granular metals. All results\nare valid at intermediate temperatures, E_c>>T/g_T>\\delta, where \\delta is the\nmean energy level spacing for a single grain and E_c its charging energy. We\nshow that the electron-electron interaction leads to an increase of the\nthermopower with decreasing grain size and discuss our results in the light of\nfuture generation thermoelectric materials for low temperature applications.\nThe behavior of the figure of merit depending on system parameters like grain\nsize, tunneling conductance, and temperature is presented.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nanoelectromechanics of shuttle devices: A single-electron tunneling (SET) device with a nanoscale central island that\ncan move with respect to the bulk source- and drain electrodes allows for a\nnanoelectromechanical (NEM) coupling between the electrical current through the\ndevice and mechanical vibrations of the island. Although an electromechanical\n\"shuttle\" instability and the associated phenomenon of single-electron\nshuttling were predicted more than 15 years ago, both theoretical and\nexperimental studies of NEM-SET structures are still carried out. New\nfunctionalities based on quantum coherence, Coulomb correlations and coherent\nelectron-spin dynamics are of particular current interest. In this article we\npresent a short review of recent activities in this area.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Geometrical meaning of winding number and its characterization of\n  topological phases in one-dimensional chiral non-Hermitian systems: We unveil the geometrical meaning of winding number and utilize it to\ncharacterize the topological phases in one-dimensional chiral non-Hermitian\nsystems. While chiral symmetry ensures the winding number of Hermitian systems\nbeing integers, it can take half integers for non-Hermitian systems. We give a\ngeometrical interpretation of the half integers by demonstrating that the\nwinding number $\\nu$ of a non-Hermitian system is equal to half of the\nsummation of two winding numbers $\\nu_1$ and $\\nu_2$ associated with two\nexceptional points respectively. The winding numbers $\\nu_1$ and $\\nu_2$\nrepresent the times of real part of the Hamiltonian in momentum space\nencircling the exceptional points and can only take integers. We further find\nthat the difference of $\\nu_1$ and $\\nu_2$ is related to the second winding\nnumber or energy vorticity. By applying our scheme to a non-Hermitian\nSu-Schrieffer-Heeger model and an extended version of it, we show that the\ntopologically different phases can be well characterized by winding numbers.\nFurthermore, we demonstrate that the existence of left and right zero-mode edge\nstates is closely related to the winding number $\\nu_1$ and $\\nu_2$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Intrinsic giant Stark effect of boron-carbon-nitride nanoribbons with\n  zigzag edges: Electronic properties of zigzag boron-carbon-nitride (BCN) nanoribbons, where\nthe outermost C atoms on the edges of graphene nanoribbons are replaced by B or\nN atoms, are theoretically studied using the first-principles calculations. We\nshow that BCN nanoribbons are metallic, since several bands cross the Fermi\nlevel. For BCN nanoribbons in a rich H$_2$ environment, the so-called nearly\nfree electron state appears just above the Fermi level because of the intrinsic\ngiant Stark effect due to the internal electric field of a transverse dipole\nmoment. The position of the nearly free electron state can be controlled by\napplying an electric field parallel to the dipole moment. The hydrogenation of\nthe nitrogen atom is necessary for the appearance of the giant Stark effect in\nBCN nanoribbons. We also discuss the effect of stacking order on the intrinsic\ngiant Stark effect in bilayer BCN nanoribbons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Kondo effect in coupled quantum dots with RKKY interaction: Finite\n  temperature and magnetic field effects: We study transport through two quantum dots coupled by an RKKY interaction as\na function of temperature and magnetic field. By applying the Numerical\nRenormalization Group (NRG) method we obtain the transmission and the linear\nconductance. At zero temperature and magnetic field, we observe a quantum phase\ntransition between the Kondo screened state and a local spin singlet as the\nRKKY interaction is tuned. Above the critical RKKY coupling the Kondo peak is\nsplit. However, we find that both finite temperature and magnetic field restore\nthe Kondo resonance. Our results agree well with recent transport experiments\non gold grain quantum dots in the presence of magnetic impurities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Skyrmion dynamics in quantum Hall ferromagnets: Exploring a classical solution of the non-linear sigma model for a quantum\nHall ferromagnet, a skyrmion-magnon effective hamiltonian is obtained via the\ncollective coordinates method. Using the Feynman-Vernon functional integral\nformalism for this model we find the temperature dependent transport\ncoefficients which characterize a single skyrmion dynamics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic transport of folded graphene nanoribbons: We investigate the electronic transport properties of a folded graphene\nnanoribbon with monolayer nanoribbon contacts. We consider two possible\nfoldings: either the nanoribbon can be folded onto itself in the shape of a\nhairpin with the nanoribbon leads at a $0^\\circ$ angle, or the monolayer\ncontacts have different directions, forming a $60^\\circ$ angle. The system is\ndescribed by a single $\\pi$-band nearest-neighbor tight-binding Hamiltonian\ntaking into account curvature effects. We have found that for the case of a\nnanoribbon folded over itself the conductance oscillates from almost zero and a\nfinite value depending on the coupling between contacts, whereas in the\n$60^\\circ$ angle folding the conductance is only slightly perturbed, allowing\nfor the connection of graphene nanoelectronic components in a variety of\ngeometries.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Intrinsic spin-orbit torque in an antiferromagnet with a weakly\n  noncollinear spin configuration: An antiferromagnet is a promising material for spin-orbit torque generation.\nEarlier studies of the spin-orbit torque in an antiferromagnet are limited to\ncollinear spin configurations. We calculate the spin-orbit torque in an\nantiferromagnet whose spin ordering is weakly noncollinear. Such\nnoncollinearity may be induced spontaneously during the magnetization dynamics\neven when the equilibrium spin configuration is perfectly collinear. It is\nshown that deviation from perfect collinearity can modify properties of the\nspin-orbit torque since noncollinearity generates extra Berry phase\ncontributions to the spin-orbit torque, which are forbidden for collinear spin\nconfigurations. In sufficiently clean antiferromagnets, this modification can\nbe significant. We estimate this effect to be of relevance for fast\nantiferromagnetic domain wall motion.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetoplasmon excitations in arrays of circular and noncircular quantum\n  dots: We have investigated the magnetoplasmon excitations in arrays of circular and\nnoncircular quantum dots within the Thomas-Fermi-Dirac-von Weizs\\\"acker\napproximation. Deviations from the ideal collective excitations of isolated\nparabolically confined electrons arise from local perturbations of the\nconfining potential as well as interdot Coulomb interactions. The latter are\nunimportant unless the interdot separations are of the order of the size of the\ndots. Local perturbations such as radial anharmonicity and noncircular symmetry\nlead to clear signatures of the violation of the generalized Kohn theorem. In\nparticular, the reduction of the local symmetry from SO(2) to $C_4$ results in\na resonant coupling of different modes and an observable anticrossing behaviour\nin the power absorption spectrum. Our results are in good agreement with recent\nfar-infrared (FIR) transmission experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Theoretical Study of Electrical Conduction Through a Molecule Connected\n  to Metallic Nanocontacts: We present a theoretical study of electron transport through a molecule\nconnected to two metallic nanocontacts. The system investigated is 1,4\nbenzene-dithiolate (BDT) chemically bonded to two Au contacts. The surface\nchemistry is modeled by representing the tips of the Au contacts as two atomic\nclusters and treating the molecule-cluster complex as a single entity in an\nextended Huckel tight binding scheme. We model the tips using several different\ncluster geometries. An ideal lead is attached to each cluster, and the lead to\nlead transmission is calculated. The role of the molecule-cluster interaction\nin transport is analyzed by using single channel leads. We then extend the\ncalculations to multi-channel leads that are a more realistic model of the\ntip's environment. Using the finite-voltage, finite temperature Landauer\nformula, we calculate the differential conductance for the different systems\nstudied. The similarities and differences between the predictions of the\npresent class of models and recent experimental work are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Kondo physics in tunable semiconductor nanowire quantum dots: We have observed the Kondo effect in strongly coupled semiconducting nanowire\nquantum dots. The devices are made from indium arsenide nanowires, grown by\nmolecular beam epitaxy, and contacted by titanium leads. The device\ntransparency can be tuned by changing the potential on a gate electrode, and\nfor increasing transparencies the effects dominating the transport changes from\nCoulomb Blockade to Universal Conductance Fluctuations with Kondo physics\nappearing in the intermediate region.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Peierls-type Instability and Tunable Band Gap in Functionalized Graphene: Functionalizing graphene was recently shown to have a dramatic effect on the\nelectronic properties of this material. Here we investigate spatial ordering of\nadatoms driven by the RKKY-type interactions. In the ordered state, which\narises via a Peierls-instability-type mechanism, the adatoms reside mainly on\none of the two graphene sublattices. Bragg scattering of electron waves induced\nby sublattice symmetry breaking results in a band gap opening, whereby Dirac\nfermions acquire a finite mass. The band gap is found to be immune to the\nadatoms' positional disorder, with only an exponentially small number of\nlocalized states residing in the gap. The gapped state is stabilized in a wide\nrange of electron doping. Our findings show that controlled adsorption of\nadatoms or molecules provides a route to engineering a tunable band gap in\ngraphene.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Terahertz lasing from intersubband polariton-polariton scattering in\n  asymmetric quantum wells: Electric dipole transitions between different cavity polariton branches or\nbetween dressed atomic states with the same excitation number are strictly\nforbidden in centro-symmetric systems. For doped quantum wells in semiconductor\nmicrocavities, the strong coupling between an intersubband transition in the\nconduction band and a cavity mode produces two branches of intersubband cavity\npolaritons, whose normal-mode energy splitting is tunable and can be in the\nterahertz region. Here, we show that, by using asymmetric quantum wells, it is\npossible to have allowed dipolar transitions between different polaritonic\nbranches, leading to the emission of terahertz photons. We present a quantum\nfield theory for such a system and predict that high-efficiency, widely tunable\nterahertz lasing can be obtained.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Detection of quantum interference without interference: Quantum interference is typically detected through the dependence of the\ninterference signal on certain parameters (path length, Aharonov-Bohm flux,\netc.), which can be varied in a controlled manner. The destruction of\ninterference by a which-path measurement is a paradigmatic manifestation of\nquantum effects. Here we report on a novel measurement protocol that realizes\ntwo objectives: (i) certifying that a measured signal is the result of\ninterference avoiding the need to vary parameters of the underlying\ninterferometer, and (ii) certifying that the interference signal at hand is of\nquantum nature. In particular, it yields a null outcome in the case of\nclassical interference. Our protocol comprises measurements of\ncross-correlations between the readings of which-path weakly coupled detectors\npositioned at the respective interferometer's arms and the current in one of\nthe interferometer's drains. We discuss its implementation with an\nexperimentally available platform: an electronic Mach-Zehnder interferometer\n(MZI) coupled electrostatically to \"detectors\" (quantum point contacts).",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermodynamics of a Single Mesoscopic Phononic Mode: In recent decades, the laws of thermodynamics have been pushed down to\nsmaller and smaller scales, within the field of stochastic thermodynamics and\nstate-of-art experiments performed on mesoscopic systems. These measurements\nconcern electrons, photons, and mesoscopic mechanical objects. Here we report\non the measurements of thermal fluctuations of a single mechanical mode\nin-equilibrium with a heat reservoir. The device under study is a\nnanomechanical beam with a first flexure resonating at 3.8MHz, cooled down to\ntemperatures in the range from 100mK to 400mK. The technique is constructed\naround a microwave opto-mechanical setup using a cryogenic High Electron\nMobility Transistor, and is based on two parametric amplifications implemented\nin series: an in-built opto-mechanical 'blue-detuned' pumping plus a Traveling\nWave Parametric Amplifier stage. We demonstrate our ability to resolve energy\nfluctuations of the mechanical mode in real-time up to the fastest relevant\nspeed given by the mechanical relaxation rate. The energy probability\ndistribution is then exponential, matching the expected Boltzmann distribution.\nThe variance of fluctuations is found to be $(k_B T)^2$ with no free\nparameters. Our microwave detection floor is about 3 Standard Quantum Limit at\n6GHz; the resolution of our fastest acquisition tracks reached about 100\nphonons, and is related to the rather poor opto-mechanical coupling of the\ndevice ($g_0/2\\pi\\approx 0.5~$Hz). This result is deeply in the classical\nregime, but shall be extended to the quantum case in the future with systems\npresenting a much larger $g_0$ (up to $2\\pi\\times 250~$Hz), potentially\nreaching the resolution of a single mechanical quantum. We believe that it will\nopen a new experimental field: phonon-based quantum stochastic thermodynamics,\nwith fundamental implications for quantum heat transport and macroscopic\nmechanical quantum coherence.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Unexpected Gaussian line shapes reveal electron-adsorbate interaction as\n  dominant broadening mechanism in quantum corrals: Understanding the factors influencing the lifetime of electronic states in\nartificial quantum structures is of great significance for advancing quantum\ntechnologies. This study focuses on CO-based quantum corrals on Cu(111).\nTunneling spectroscopy measurements reveal a strong correlation between the\nsize of the quantum corral and spectral width, characterized by a predominant\nGaussian line shape. We attribute this dominant Gaussian-shaped lifetime\nbroadening to the interaction of surface state electrons with the corral\nboundary. To further investigate this phenomenon, we constructed corrals of\nvarying wall densities. Our findings indicate that elastic processes, such as\ntunneling, are more sensitive to wall density than coupling to the bulk.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fast, low-current spin-orbit torque switching of magnetic tunnel\n  junctions through atomic modifications of the free layer interfaces: Future applications of spin-orbit torque will require new mechanisms to\nimprove the efficiency for switching nanoscale magnetic tunnel junctions\n(MTJs), while also controlling the magnetic dynamics to achieve fast,\nnanosecond scale performance with low write error rates. Here we demonstrate a\nstrategy to simultaneously enhance the interfacial magnetic anisotropy energy\nand suppress interfacial spin memory loss by introducing sub-atomic and\nmonatomic layers of Hf at the top and bottom interfaces of the ferromagnetic\nfree layer of an in-plane magnetized three-terminal MTJ device. When combined\nwith a beta-W spin Hall channel that generates spin-orbit torque, the\ncumulative effect is a switching current density of 5.4 x 106 A/cm2, more than\na factor of 3 lower than demonstrated in any other spin-orbit-torque magnetic\nmemory device at room temperature, and highly reliable switching with current\npulses only 2 ns long.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Onset of optical-phonon cooling in multilayer graphene revealed by RF\n  noise and black-body radiation thermometries: We report on electron cooling power measurements in few-layer graphene\nexcited by Joule heating by means of a new setup combining electrical and\noptical probes of the electron and phonon baths temperatures. At low bias,\nnoise thermometry allows us to retrieve the well known acoustic phonon cooling\nregimes below and above the Bloch Gr\\\"uneisen temperature, with additional\ncontrol over the phonon bath temperature. At high electrical bias, we show the\nrelevance of direct optical investigation of the electronic temperature by\nmeans of black-body radiation measurements that provide higher accuracy than\nnoise thermometry. In this regime, the onset of new efficient relaxation\npathways involving optical modes is observed",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Demonstration of Entanglement of Electrostatically Coupled\n  Singlet-Triplet Qubits: Quantum computers have the potential to solve certain interesting problems\nsignificantly faster than classical computers. To exploit the power of a\nquantum computation it is necessary to perform inter-qubit operations and\ngenerate entangled states. Spin qubits are a promising candidate for\nimplementing a quantum processor due to their potential for scalability and\nminiaturization. However, their weak interactions with the environment, which\nleads to their long coherence times, makes inter-qubit operations challenging.\nWe perform a controlled two-qubit operation between singlet-triplet qubits\nusing a dynamically decoupled sequence that maintains the two-qubit coupling\nwhile decoupling each qubit from its fluctuating environment. Using state\ntomography we measure the full density matrix of the system and determine the\nconcurrence and the fidelity of the generated state, providing proof of\nentanglement.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Confinement and Fermion Doubling Problem in Dirac-like Hamiltonians: We investigate the interplay between confinement and the fermion doubling\nproblem in Dirac-like Hamiltonians. Individually, both features are well known.\nFirst, simple electrostatic gates do not confine electrons due to the Klein\ntunneling. Second, a typical lattice discretization of the first-order\nderivative $k \\rightarrow -i\\partial_x$ skips the central point and allow\nspurious low-energy, highly oscillating solutions known as fermion doublers.\nWhile a no-go theorem states that the doublers cannot be eliminated without\nartificially breaking a symmetry, here we show that the symmetry broken by the\nWilson's mass approach is equivalent to the enforcement of hard-wall boundary\nconditions, thus making the no-go theorem irrelevant when confinement is\nforeseen. We illustrate our arguments by calculating the following: (i) the\nband structure and transport properties across thin films of the topological\ninsulator Bi$_2$Se$_3$, for which we use ab-initio density functional theory\ncalculations to justify the model; and (ii) the band structure of zigzag\ngraphene nanoribbons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ion-beam nanopatterning of silicon surfaces under co-deposition of\n  non-silicide-forming impurities: We report experiments on surface nanopatterning of Si targets which are\nirradiated with 2 keV Ar + ions impinging at near-glancing incidence, under\nconcurrent co-deposition of Au impurities simultaneously extracted from a gold\ntarget by the same ion beam. Previous recent experiments by a number of groups\nsuggest that silicide formation is a prerequisite for pattern formation in the\npresence of metallic impurities. In spite of the fact that Au is known not to\nform stable compounds with the Si atoms, ripples nonetheless emerge in our\nexperiments with nanometric wavelengths and small amplitudes, and with an\norientation that changes with distance to the Au source. We provide results of\nsample analysis through Auger electron and energy-dispersive X-ray\nspectroscopies for their space-resolved chemical composition, and through\natomic force, scanning transmission electron, and high-resolution transmission\nmicroscopies for their morphological properties. We discuss these findings in\nthe light of current continuum models for this class of systems. The\ncomposition of and the dynamics within the near-surface amorphized layer that\nensues is expected to play a relevant role to account for the unexpected\nformation of these surface structures.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Lateral plasmonic crystals: Tunability, dark modes, and weak-to-strong\n  coupling transition: We study transmission of the terahertz radiation through a two-dimensional\nelectron gas with a concentration controlled by grating gate electrodes.\nVoltage applied to these electrodes creates a lateral plasmonic crystal with a\ngate-tunable band structure. We find that only a part of plasmonic modes of\nsuch a crystal is seen in the transmission spectrum for the case of homogeneous\nexcitation (so-called bright modes), while there also exist dark modes which\nshow up only in a case of inhomogeneous excitation. We develop a theory that\ndescribes both weak- to strong- coupling transition in the crystal with\nincreasing depth of the density modulation and a transition from resonant to\nsuper-resonant regime with increasing quality factor of the structure. We\ndiscuss very recent experiment, where transmission of the terahertz radiation\nthrough GaN/AlGaN based grating gate periodic structures was studied. We argue\nthat this experiment represents an evidence of formation of the lateral\nplasmonic crystal with the band structure fully controlled by the gate\nelectrodes and magnetic field, in a full agreement with developed theory.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "On the possibility of the fractional ac Josephson effect in\n  non-topological conventional superconductor-normal-superconductor junctions: Topological superconductors supporting Majorana Fermions with non-abelian\nstatistics are presently a subject of intense theoretical and experimental\neffort. It has been proposed that the observation of a half-frequency or a\nfractional Josephson effect is a more reliable test for topological\nsuperconductivity than the search for end zero modes. Low-energy end modes can\noccur accidentally due to impurities. In fact, the fractional Josephson effect\nhas been observed for the semiconductor nanowire system. Here we consider the\nac Josephson effect in a conventional s-wave superconductor-normal\nmetal-superconductor junction at a finite voltage. Using a Floquet-Keldysh\ntreatment of the finite voltage junction, we show that the power dissipated\nfrom the junction, which measures the ac Josephson effect, can show a peak at\nhalf (or even incommensurate fractions) of the Josephson frequency. A similar\nconclusion is shown to hold for the Shapiro step measurement. The ac fractional\nJosephson peak can also be understood simply in terms of Landau-Zener processes\nassociated with the Andreev bound state spectrum of the junction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Phononic bandgap nano-acoustic cavity with ultralong phonon lifetime: We present measurements at millikelvin temperatures of the\nmicrowave-frequency acoustic properties of a crystalline silicon nanobeam\ncavity incorporating a phononic bandgap clamping structure for acoustic\nconfinement. Utilizing pulsed laser light to excite a co-localized optical mode\nof the nanobeam cavity, we measure the dynamics of cavity acoustic modes with\nsingle-phonon sensitivity. Energy ringdown measurements for the fundamental\n$5$~GHz acoustic mode of the cavity shows an exponential increase in phonon\nlifetime versus number of periods in the phononic bandgap shield, increasing up\nto $\\tau \\approx 1.5$~seconds. This ultralong lifetime, corresponding to an\neffective phonon propagation length of several kilometers, is found to be\nconsistent with damping from non-resonant two-level system defects on the\nsurface of the silicon device. Potential applications of these ultra-coherent\nnanoscale mechanical resonators range from tests of various collapse models of\nquantum mechanics to miniature quantum memory elements in hybrid\nsuperconducting quantum circuits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron cooling with graphene-insulator-superconductor tunnel junctions\n  and applications to fast bolometry: Electronic cooling in hybrid normal metal-insulator-superconductor junctions\nis a promising technology for the manipulation of thermal loads in solid state\nnanosystems. One of the main bottlenecks for efficient electronic cooling is\nthe electron-phonon coupling, as it represents a thermal leakage channel to the\nphonon bath. Graphene is a two-dimensional material that exhibits a weaker\nelectron-phonon coupling compared to standard metals. For this reason, we study\nthe electron cooling in graphene-based systems consisting of a graphene sheet\ncontacted by two insulator/superconductor junctions. We show that, by properly\nbiasing the graphene, its electronic temperature can reach base values lower\nthan those achieved in similar systems based on metallic ultra-thin films.\nMoreover, the lower electron-phonon coupling is mirrored in a lower heat power\npumped into the superconducting leads, thus avoiding their overheating and\npreserving the cooling mechanisms. Finally, we analyze the possible application\nof cooled graphene as a bolometric radiation sensor. We study its main figures\nof merit, i.e. responsivity, noise equivalent power and response time. In\nparticular, we show that the built-in electron refrigeration allows reaching a\nresponsivity of the order of 50 nA/pW and a noise equivalent power of order of\n$\\rm 10^{-18}\\, W\\, Hz^{-1/2}$ while the response speed is about 10 ns,\ncorresponding to a thermal bandwidth in the order of 20MHz.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Phonon wave packet emission during state preparation of a semiconductor\n  quantum dot using different schemes: The carrier-phonon interaction in semiconductor quantum dots can greatly\naffect the optical preparation of the excited state. For resonant excitation\nused in the Rabi preparation scheme, the polaron is formed accompanied by the\nemission of a phonon wave packet, leading to a degradation of preparation\nfidelity. In this paper, phonon wave packets for different coherent excitation\nschemes are analyzed. One example is the adiabatic rapid passage scheme relying\non a chirped excitation. Here, also a phonon wave packet is emitted, but the\npreparation fidelity can still be approximately unity. A focus is on the phonon\nimpact on a recently proposed swing-up scheme, induced by two detuned pulses.\nSimilar to the Rabi scheme, a degradation and a phonon wave packet emission is\nfound, despite the detuning. If the swing-up frequency coincides with the\nmaximum of the phonon spectral density, a series of wave packets is emitted\nyielding an even stronger degradation. The insight gained from our results will\nfurther help in designing an optimal preparation scheme for quantum dots.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Imaging electron flow from collimating contacts in graphene: The ballistic motion of electrons in graphene encapsulated in hexagonal boron\nnitride (hBN) promises exciting opportunities for electron-optics devices. A\nnarrow electron beam is desired, with both the mean free path and coherence\nlength exceeding the device size. One can form a collimating contact in\ngraphene by adding zigzag contacts on either side of the electron emitter that\nabsorb stray electrons to form a collimated electron beam [23]. Here we provide\nimages of electron flow from a collimating contact that directly show the width\nand shape of the electron beam, obtained using a Scanning Gate Microscope (SGM)\ncooled to 4.2 K. The device is a hBN-encapsulated graphene hall bar with narrow\nside contacts on either side of the channel that have an electron emitter at\nthe end and absorbing zig-zag contacts at both side. To form an image of\nelectron flow, the SGM tip is raster scanned at a constant height above the\nsample surface while the transmission to a receiving contact on opposite sides\nof the channel is measured. By displaying the change {\\Delta}T vs. tip\nposition, an image of ballistic flow is obtained. The angular width of the\nelectron beam leaving the collimating contact is found by applying a\nperpendicular magnetic field B that bends electron paths into cyclotron orbits.\nSGM images reveal that electron flow from a collimating contact disappears\nquickly at B = 0.05T while the flow from a non-collimating contact persists up\nto B = 0.19 T. Ray tracing simulations agree well with the experimental images\nover a range of B and electron density n. By fitting the half-width at half-max\n(HWHM) of the magnitude of electron flow in the experimental SGM images, we\nfind a narrow half angular width {\\Delta}{\\theta} = 9.2{\\deg} for the electron\nflow from the collimating contact, compared with a wide flow {\\Delta}{\\theta} =\n54{\\deg} from the non-collimating contact.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic bandstructure and optical gain of lattice matched III-V\n  dilute nitride bismide quantum wells for 1.55 $\u03bc$m optical communication\n  systems: Dilute nitride bismide GaNBiAs is a potential semiconductor alloy for near-\nand mid-infrared applications, particularly in 1.55 $\\mu$m optical\ncommunication systems. Incorporating dilute amounts of Bismuth (Bi) into GaAs\nreduces the effective bandgap rapidly, while significantly increasing the\nspin-orbit-splitting energy. Additional incorporation of dilute amounts of\nNitrogen (N) helps to attain lattice matching with GaAs, while providing a\nroute for flexible bandgap tuning. Here we present a study of the electronic\nbandstructure and optical gain of the lattice matched\nGaN$_x$Bi$_y$As$_{1-x-y}$/GaAs quaternary alloy quantum well (QW) based on the\n16-band k$\\cdot$p model. We have taken into consideration the interactions\nbetween the N and Bi impurity states with the host material based on the band\nanticrossing (BAC) and valence band anticrossing (VBAC) model. The optical gain\ncalculation is based on the density matrix theory. We have considered different\nlattice matched GaNBiAs QW cases and studied their energy dispersion curves,\noptical gain spectrum, maximum optical gain and differential gain; and compared\ntheir performances based on these factors. The thickness and composition of\nthese QWs were varied in order to keep the emission peak fixed at 1.55 $\\mu$m.\nThe well thickness has an effect on the spectral width of the gain curves. On\nthe other hand, a variation in the injection carrier density has different\neffects on the maximum gain and differential gain of QWs of varying\nthicknesses. Among the cases studied, we found that the 6.3 nm thick\nGaN$_3$Bi$_{5.17}$As$_{91.83}$ lattice matched QW was most suited for 1.55\n$\\mu$m (0.8 eV) GaAs-based photonic applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Sideband ground-state cooling of graphene with Rydberg atoms via vacuum\n  forces: We present a scheme leading to ground-state cooling of the fundamental\nout-of-plane (flexural) mode of a suspended graphene sheet. Our proposal\nexploits the coupling between a driven Rydberg atom and the graphene resonator,\nwhich is enabled by vacuum forces. Thanks to the large atomic polarizability of\nthe Rydberg states, the Casimir-Polder force is several orders of magnitude\nlarger than the corresponding force achieved for atoms in the ground state. By\nplaying with the distance between the atom and the graphene membrane, we show\nthat resolved sideband cooling is possible, bringing the occupation number of\nthe fundamental flexural mode down to its quantum limit. Our findings are\nexpected to motivate physical applications of graphene at extremely low\ntemperatures.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Decoupling of the many-body effects from the electron mass in GaAs by\n  means of reduced dimensionality: Determining the (bare) electron mass $m_0$ in crystals is often hindered by\nmany-body effects since Fermi-liquid physics renormalises the band mass, making\nthe observed effective mass $m^*$ depend on density. Here, we use a\none-dimensional (1D) geometry to amplify the effect of interactions, forcing\nthe electrons to form a nonlinear Luttinger liquid with separate holon and\nspinon bands, therefore separating the interaction effects from $m_0$.\nMeasuring the spectral function of gated quantum wires formed in GaAs by means\nof magnetotunnelling spectroscopy and interpreting them using the 1D\nFermi-Hubbard model, we obtain $m_0=(0.0525\\pm0.0015)m_\\textrm{e}$ in this\nmaterial, where $m_\\textrm{e}$ is the free-electron mass. By varying the\ndensity in the wires, we change the interaction parameter $r_\\textrm{s}$ in the\nrange from $\\sim$1-4 and show that $m_0$ remains constant. The determined value\nof $m_0$ is $\\sim 22$% lighter than observed in GaAs in geometries of higher\ndimensionality $D$ ($D>1$), consistent with the quasi-particle picture of a\nFermi liquid that makes electrons heavier in the presence of interactions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Probing topological protected transport in finite-sized\n  Su-Schrieffer-Heeger chains: In order to transport information with topological protection, we reveal and\ndemonstrate experimentally the existence of a characteristic length $L_c$,\ncoined as the transport length, in the bulk size for edge states in\none-dimensional Su-Schrieffer-Heeger (SSH) chains. In spite of the\ncorresponding wavefunction amplitude decays exponentially, characterized by the\npenetration depth $\\xi$, the transport between two edge states remains possible\neven when the lattice size $L$ is much larger than the penetration depth, i.e.,\n$\\xi \\ll L \\le L_c$. Due to the non-zero coupling energy in a finite-size\nsystem, the supported SSH edge states are not completely isolated at the two\nends, giving an abrupt change in the wave localization, manifested through the\ninverse participation ratio to the lattice size. To verify such a\nnon-exponential scaling factor to the system size, we implement a chain of\nsplit-ring resonators and their complementary ones with controllable hopping\nstrengths. By performing the measurements on the group velocity from the\ntransmission spectroscopy of non-trivially topological edge states with pulse\nexcitations, the transport velocity between two edge states is directly\nobserved with the number of lattices up to $20$. Along the route to harness\ntopology to protect optical information, our experimental demonstrations\nprovide a crucial guideline for utilizing photonic topological devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A study on the universality of the magnetic-field-induced phase\n  transitions in the two-dimensional electron system in an AlGaAs/GaAs\n  heterostructure: Plateau-plateau (P-P) and insulator-quantum Hall conductor (I-QH) transitions\nare observed in the two-dimensional electron system in an AlGaAs/GaAs\nheterostructure. At high fields, the critical conductivities are not of the\nexpected universal values and the temperature-dependence of the width of the\nP-P transition does not follow the universal scaling. However, the semicircle\nlaw still holds, and universal scaling behavior was found in the P-P transition\nafter mapping it to the I-QH transition by the Landau-level addition\ntransformation. We pointed out that in order to get a correct critical\nexponent, it is essential that the scaling analysis must be performed near the\ncritical point. And with proper analysis, we found that the P-P transition and\nthe insulator quantum Hall conductor transitions are of the same universal\nclass.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current noise of a superconducting single electron transistor coupled to\n  a resonator: We analyze the current and zero-frequency current noise properties of a\nsuperconducting single electron resonator (SSET) coupled to a resonator,\nfocusing on the regime where the SSET is operated in the vicinity of the\nJosephson quasiparticle resonance. We consider a range of coupling strengths\nand resonator frequencies to reflect the fact that in practice the system can\nbe tuned to quite a high degree with the resonator formed either by a\nnanomechanical oscillator or a superconducting stripline fabricated in close\nproximity to the SSET. For very weak couplings the SSET acts on the resonator\nlike an effective thermal bath. In this regime the current characteristics of\nthe SSET are only weakly modified by the resonator. Using a mean field\napproach, we show that the current noise is nevertheless very sensitive to the\ncorrelations between the resonator and the SSET charge. For stronger couplings,\nthe SSET can drive the resonator into limit cycle states where self-sustained\noscillation occurs and we find that regions of well-defined bistability exist.\nDynamical transitions into and out of the limit cycle state are marked by\nstrong fluctuations in the resonator energy, but these fluctuations are\nsuppressed within the limit cycle state. We find that the current noise of the\nSSET is strongly influenced by the fluctuations in the resonator energy and\nhence should provide a useful indicator of the resonator's dynamics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetotransport in graphene on silicon side of SiC: We have studied the transport properties of graphene grown on silicon side of\nSiC. Samples under study have been prepared by two different growth methods in\ntwo different laboratories. Magnetoresistance and Hall resistance have been\nmeasured at temperatures between 4 and 100 K in resistive magnet in magnetic\nfields up to 22 T. In spite of differences in sample preparation, the field\ndependence of resistances measured on both sets of samples exhibits two periods\nof magneto-oscillations indicating two different parallel conducting channels\nwith different concentrations of carriers. The semi-quantitative agreement with\nthe model calculation allows for conclusion that channels are formed by\nhigh-density and low-density Dirac carriers. The coexistence of two different\ngroups of carriers on the silicon side of SiC was not reported before.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Resonant single and multi-photon coherent transitions in a detuned\n  regime: We performed quantum manipulations of the multi-level spin system S=5/2 of a\nMn$^{2+}$ ion, by means of a two-tone pulse drive. The detuning between the\nexcitation and readout radio frequency pulses allows one to select the number\nof photons involved in a Rabi oscillation as well as increase the frequency of\nthis nutation. Thus detuning can lead to a resonant multi-photon process. Our\nanalytical model for a two-photon process as well as a numerical generalization\nfit well the experimental findings, with implications in the use of multi-level\nspin systems as tunable solid state qubits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Self-Focusing Skyrmion Racetracks in Ferrimagnets: We theoretically study the dynamics of ferrimagnetic skyrmions in\ninhomogeneous metallic films close to the angular momentum compensation point.\nIn particular, it is shown that the line of the vanishing angular momentum can\nbe utilized as a self-focusing racetrack for skyrmions. To that end, we begin\nby deriving the equations of motion for the dynamics of collinear ferrimagnets\nin the presence of a charge current. The obtained equations of motion reduce to\nthose of ferromagnets and antiferromagnets at two special limits. In the\ncollective coordinate approach, a skyrmion behaves as a massive charged\nparticle moving in a viscous medium subjected to a magnetic field. Analogous to\nthe snake orbits of electrons in a nonuniform magnetic field, we show that a\nferrimagnet with the nonuniform angular momentum density can exhibit snake\ntrajectories of skyrmions, which can be utilized as racetracks for skyrmions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamics of hole singlet triplet qubits with large g-factor differences: The spin-orbit interaction is the key element for electrically tunable spin\nqubits. Here we probe the effect of cubic Rashba spin-orbit interaction on\nmixing of the spin states by investigating singlet-triplet oscillations in a\nplanar Ge hole double quantum dot. By varying the magnetic field direction we\nfind an intriguing transformation of the funnel into a butterfly-shaped\npattern. Landau-Zener sweeps disentangle the Zeeman mixing effect from the\nspin-orbit induced coupling and show that large singlet-triplet avoided\ncrossings do not imply a strong spin-orbit interaction. Our work emphasizes the\nneed for a complete knowledge of the energy landscape when working with hole\nspin qubits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bilayer graphene: gap tunability and edge properties: Bilayer graphene -- two coupled single graphene layers stacked as in graphite\n-- provides the only known semiconductor with a gap that can be tuned\nexternally through electric field effect. Here we use a tight binding approach\nto study how the gap changes with the applied electric field. Within a parallel\nplate capacitor model and taking into account screening of the external field,\nwe describe real back gated and/or chemically doped bilayer devices. We show\nthat a gap between zero and midinfrared energies can be induced and externally\ntuned in these devices, making bilayer graphene very appealing from the point\nof view of applications. However, applications to nanotechnology require\ncareful treatment of the effect of sample boundaries. This being particularly\ntrue in graphene, where the presence of edge states at zero energy -- the Fermi\nlevel of the undoped system -- has been extensively reported. Here we show that\nalso bilayer graphene supports surface states localized at zigzag edges. The\npresence of two layers, however, allows for a new type of edge state which\nshows an enhanced penetration into the bulk and gives rise to band crossing\nphenomenon inside the gap of the biased bilayer system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Manipulation of edge states in microwave artificial graphene: Edge states are one important ingredient to understand transport properties\nof graphene nanoribbons. We study experimentally the existence and the internal\nstructure of edge states under uniaxial strain of the three main edges: zigzag,\nbearded, and armchair. The experiments are performed on artificial microwave\ngraphene flakes, where the wavefunctions are obtained by direct imaging. We\nshow that uniaxial strain can be used to manipulate the edge states: a single\nparameter controls their existence and their spatial extension into the ribbon.\nBy combining tight-binding approach and topological arguments, we provide an\naccurate description of our experimental findings. A new type of zero-energy\nstate appearing at the intersection of two edges, namely the corner state, is\nalso observed and discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Direct electronic measurement of the spin Hall effect: The generation, manipulation and detection of spin-polarized electrons in\nnanostructures define the main challenges of spin-based electronics[1]. Amongst\nthe different approaches for spin generation and manipulation, spin-orbit\ncoupling, which couples the spin of an electron to its momentum, is attracting\nconsiderable interest. In a spin-orbit-coupled system, a nonzero spin-current\nis predicted in a direction perpendicular to the applied electric field, giving\nrise to a \"spin Hall effect\"[2-4]. Consistent with this effect,\nelectrically-induced spin polarization was recently detected by optical\ntechniques at the edges of a semiconductor channel[5] and in two-dimensional\nelectron gases in semiconductor heterostructures[6,7]. Here we report\nelectrical measurements of the spin-Hall effect in a diffusive metallic\nconductor, using a ferromagnetic electrode in combination with a tunnel barrier\nto inject a spin-polarized current. In our devices, we observe an induced\nvoltage that results exclusively from the conversion of the injected spin\ncurrent into charge imbalance through the spin Hall effect. Such a voltage is\nproportional to the component of the injected spins that is perpendicular to\nthe plane defined by the spin current direction and the voltage probes. These\nexperiments reveal opportunities for efficient spin detection without the need\nfor magnetic materials, which could lead to useful spintronics devices that\nintegrate information processing and data storage.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Exciton-phonon-scattering: A competition between bosonic and fermionic\n  nature of bound electron-hole pairs: The question of macroscopic occupation and spontaneous emergence of coherence\nfor exciton ensembles has gained renewed attention due to the rise of van der\nWaals heterostructures made of atomically thin semiconductors. The hosted\ninterlayer excitons exhibit nanosecond lifetimes, long enough to allow for\nexcitonic thermalization in time. Several experimental studies reported\nsignatures of macroscopic occupation effects at elevated exciton densities.\nWith respect to theory, excitons are composite particles formed by fermionic\nconstituents, and a general theoretical argument for a bosonic thermalization\nof an exciton gas beyond the linear regime is still missing. Here, we derive an\nequation for the phonon mediated thermalization at densities above the\nclassical limit, and identify which conditions favor the thermalization of\nfermionic or bosonic character, respectively. In cases where acoustic,\nquasielastic phonon scattering dominates the dynamics, our theory suggests that\ntransition metal dichalcogenide (TMDC) excitons might be bosonic enough to show\nbosonic thermalization behaviour and decreasing dephasing for increasing\nexciton densities. This can be interpreted as a signature of an emerging\ncoherence in the exciton ground state, and agrees well with the experimentally\nobserved features, such as a decreasing linewidth for increasing densities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-orbit coupling and the static polarizability of single-wall carbon\n  nanotubes: We calculate the static longitudinal polarizability of single-wall carbon\nnanotubes in the long wavelength limit taking into account spin-orbit effects.\nWe use a four-orbital orthogonal tight-binding formalism to describe the\nelectronic states and the random phase approximation to calculate the\ndielectric function. We study the role of both the Rashba as well as the\nintrinsic spin-orbit interactions on the longitudinal dielectric response, i.e.\nwhen the probing electric field is parallel to the nanotube axis. The\nspin-orbit interaction modifies the nanotube electronic band dispersions, which\nmay especially result in a small gap opening in otherwise metallic tubes. The\nbandgap size and state features, the result of competition between Rashba and\nintrinsic spin-orbit interactions, result in drastic changes in the\nlongitudinal static polarizability of the system. We discuss results for\ndifferent nanotube types, and the dependence on nanotube radius and spin-orbit\ncouplings.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "4$\u03c0$ and 8$\u03c0$ dual Josephson effects induced by symmetry defects: In topological insulator edges, the duality between the Zeeman field\norientation and the proximitized superconducting phase has been recently\nexploited to predict a magneto-Josephson effect with a 4$\\pi$ periodicity. We\nrevisit this latter Josephson effect in the light of this duality and show that\nthe same 4$\\pi$ quantum anomaly occurs when bridging two spinless Thouless\npumps to a p-wave superconducting region that could be as small as a single and\nexperimentally-relevant superconducting quantum dot - a point-like defect. This\ninterpretation as a dual Josephson effect never requires the presence of\nMajorana modes but rather builds on the topological properties of adiabatic\nquantum pumps with Z topological invariants. It allows for the systematic\nconstruction of dual Josephson effects of arbitrary periodicity, such as 4$\\pi$\nand 8$\\pi$, by using point-like defects whose symmetry differs from that of the\npump, dubbed symmetry defects. Although adiabatic quantum pumps are typically\ndiscussed via mappings to two-dimensional geometries, we show that this\nphenomenology does not have any counterpart in conventional two-dimensional\nsystems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strain-induced pseudomagnetic and scalar fields in symmetry-enforced\n  Dirac nodes: It is known that Dirac nodes can be present at high-symmetry points of\nBrillouin zone only for certain space groups. For these cases, the effect of\nstrain is treated by symmetry considerations. The dependence of strain-induced\npotentials on the strain tensor is found. In all but two cases, the\npseudomagnetic field potential is present. It can be used to control valley\ncurrents.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "TSTG II: Projected Hartree-Fock Study of Twisted Symmetric Trilayer\n  Graphene: The Hamiltonian of the magic-angle twisted symmetric trilayer graphene (TSTG)\ncan be decomposed into a TBG-like flat band Hamiltonian and a high-velocity\nDirac fermion Hamiltonian. We use Hartree-Fock mean field approach to study the\nprojected Coulomb interacting Hamiltonian of TSTG developed in C\\u{a}lug\\u{a}ru\net al. [Phys. Rev. B 103, 195411 (2021)] at integer fillings $\\nu=-3, -2, -1$\nand $0$ measured from charge neutrality. We study the phase diagram with\n$w_0/w_1$, the ratio of $AA$ and $AB$ interlayer hoppings, and the displacement\nfield, which introduces an interlayer potential $U$ and hybridizes the TBG-like\nbands with the Dirac bands. At small $U$, we find the ground states at all\nfillings $\\nu$ are in the same phases as the tensor products of a Dirac\nsemimetal with the filling $\\nu$ TBG insulator ground states, which are\nspin-valley polarized at $\\nu=-3$, and fully (partially) intervalley coherent\nat $\\nu=-2,0$ ($\\nu=-1$) in the flat bands. An exception is $\\nu=-3$ with\n$w_0/w_1 \\gtrsim 0.7$, which possibly become a metal with competing orders at\nsmall $U$ due to charge transfers between the Dirac and flat bands. At strong\n$U$ where the bandwidths exceed interactions, all the fillings $\\nu$ enter a\nmetal phase with small or zero valley polarization and intervalley coherence.\nLastly, at intermediate $U$, semimetal or insulator phases with zero\nintervalley coherence may arise for $\\nu=-2,-1,0$. Our results provide a simple\npicture for the electron interactions in TSTG systems, and reveal the\nconnection between the TSTG and TBG ground states.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum pumping in graphene: We show that graphene-based quantum pumps can tap into evanescent modes,\nwhich penetrate deeply into the device as a consequence of Klein tunneling. The\nevanescent modes dominate pumping at the Dirac point, and give rise to a\nuniversal response under weak driving for short and wide pumps, in close\nanalogy to their role for the minimal conductivity in ballistic transport. In\ncontrast, evanescent modes contribute negligibly to normal pumps. Our findings\nadd a new incentive for the exploration of graphene-based nanoelectronic\ndevices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Localized surface plasmons in a continuous and flat graphene sheet: We derive an integral equation describing surface-plasmon polaritons in\ngraphene deposited on a substrate with a planar surface and a dielectric\nprotrusion in the opposite surface of the dielectric slab. We show that the\nproblem is mathematically equivalent to the solution of a Fredholm equation,\nwhich we solve exactly. In addition, we show that the dispersion relation of\nthe localized surface plasmons is determined by the geometric parameters of the\nprotrusion alone. We also show that such system supports both even and odd\nmodes. We give the electrostatic potential and the stream plot of the\nelectrostatic field, which clearly show the localized nature of the surface\nplasmons in a continuous and flat graphene sheet.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Stabilization of single-electron pumps by high magnetic fields: We study the effect of perpendicular magnetic fields on a single-electron\nsystem with a strongly time-dependent electrostatic potential. Continuous\nimprovements to the current quantization in these electron pumps are revealed\nby high-resolution measurements. Simulations show that the sensitivity of\ntunnel rates to the barrier potential is enhanced, stabilizing particular\ncharge states. Nonadiabatic excitations are also suppressed due to a reduced\nsensitivity of the Fock-Darwin states to electrostatic potential. The\ncombination of these effects leads to significantly more accurate current\nquantization.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Even-odd effects in NSN scattering problems: Application to graphene\n  nanoribbons: We study crossed Andreev reflection (CAR) of electrons or holes in normal\nmetal-superconductor-normal metal junctions and highlight some very strong\neffects of the underlying lattice. In particular, we demonstrate that for sharp\ninterfaces and under certain, albeit generic, symmetry conditions, the CAR\nprobability exactly vanishes for an even number of atoms in the superconducting\nregion. This even-odd effect applies notably to NSN junctions made of graphene\nnano-ribbons with armchair edges and for zigzag edges with somewhat more\nrestrictive conditions. We analyze its robustness towards smoothing of the\nboundaries or doping of the sample.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effect of picosecond magnetic pulse on dynamics of electron's subbands\n  in semiconductor bilayer nanowire: We report on possibility of charge current generation in nanowire made of two\ntunnel coupled one-dimensional electron waveguides by means of single magnetic\npulse lasting up to 20 ps. Existence of interlayer tunnel coupling plays a\ncrucial role in the effect described here as it allows for hybridization of the\nwave functions localized in different layers which can be dynamically modified\nby applying a time changeable in-plane magnetic field. Results of\ntime-dependent DFT calculations performed for a bilayer nanowire confining many\nelectrons show that the effect of such magnetic hybridization relies on tilting\nof electrons' energy subbands, to the left or to the right, depending on a sign\nof time derivative of oscillating magnetic field due to the Faraday law.\nConsequently, the tilted subbands become a source of charge flow along the\nwire. Strength of such magneto-induced current oscillations may achieve even\n$0.6\\mu\\textrm{A}$ but it depends on duration of magnetic pulse as well as on\ncharge density confined in nanowire which has to be unequally distributed\nbetween both transport layers to observe this effect.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Control of Spin Dynamics of Excitons in Nanodots for Quantum Operations: This work presents a step furthering a new perspective of proactive control\nof the spin-exciton dynamics in the quantum limit. Laser manipulation of\nspin-polarized optical excitations in a semiconductor nanodot is used to\ncontrol the spin dynamics of two interacting excitons. Shaping of femtosecond\nlaser pulses keeps the quantum operation within the decoherence time.\nComputation of the fidelity of the operations and application to the complete\nsolution of a basic quantum computing algorithm demonstrate in theory the\nfeasibility of quantum control.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coupling single photons from discrete quantum emitters in WSe$_2$ to\n  lithographically defined plasmonic slot-waveguides: We report the observation of the generation and routing of single plasmons\ngenerated by localized excitons in a WSe$_2$ monolayer flake exfoliated onto\nlithographically defined Au-plasmonic waveguides. Statistical analysis of the\nposition of different quantum emitters shows that they are $(3.3 \\pm\n0.7)\\times$ more likely to form close to the edges of the plasmonic waveguides.\nBy characterizing individual emitters we confirm their single-photon character\nvia the observation of antibunching of the signal ($g^{(2)}(0) = 0.42$) and\ndemonstrate that specific emitters couple to the modes of the proximal\nplasmonic waveguide. Time-resolved measurements performed on emitters close to,\nand far away from the plasmonic nanostructures indicate that Purcell factors up\nto $15 \\pm 3$ occur, depending on the precise location of the quantum emitter\nrelative to the tightly confined plasmonic mode. Measurement of the point\nspread function of five quantum emitters relative to the waveguide with <50nm\nprecision are compared with numerical simulations to demonstrate potential for\nhigher increases of the coupling efficiency for ideally positioned emitters.\nThe integration of such strain-induced quantum emitters with deterministic\nplasmonic routing is a step toward deep-subwavelength on-chip single quantum\nlight sources.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Floquet multi-gap topology: Non-Abelian braiding and anomalous Dirac\n  string phase: Topological phases of matter span a wide area of research shaping fundamental\npursuits and offering promise for future applications. While a significant\nfraction of topological materials has been characterized using symmetry\nrequirements of wave functions, the past two years have witnessed the rise of\nnovel multi-gap dependent topological states, the properties of which go beyond\nthese approaches and are yet to be fully explored. Thriving upon these\ninsights, we report on uncharted anomalous phases and properties that can only\narise in out-of-equilibrium Floquet settings. In particular, we identify\nFloquet-induced non-Abelian braiding mechanisms, which in turn lead to a phase\ncharacterized by an anomalous Euler class, the prime example of a multi-gap\ntopological invariant. Most strikingly, we also retrieve the first example of\nan `anomalous Dirac string phase'. This gapped out-of-equilibrium phase\nfeatures an unconventional Dirac string configuration that physically manifests\nitself via anomalous edge states on the boundary. Our results therefore not\nonly provide a stepping stone for the exploration of intrinsically dynamical\nand experimentally viable multi-gap topological phases, but also demonstrate a\npowerful way to observe these non-Abelian processes notably in quantum\nsimulators.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical Probing of the Spin Polarization of the nu=5/2 Quantum Hall\n  State: We apply polarization resolved photoluminescence spectroscopy to measure the\nspin polarization of a two dimensional electron gas in perpendicular magnetic\nfield. In the vicinity of filling factor nu=5/2, we observe a sharp\ndiscontinuity in the energy of the zero Landau level emission line. We find\nthat the splitting between the two circular polarizations exhibits a sharp drop\nat nu=5/2 and is equal to the bare Zeeman energy, which resembles the behavior\nat even filling factors. We show that this behavior is consistent with filling\nfactor nu=5/2 being unpolarized.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anisotropy of spin relaxation and transverse transport in metals: Using first principles methods we explore the anisotropy of the spin\nrelaxation and transverse transport properties in bulk metals with respect to\nthe direction of the spin quantization axis in paramagnets or of the\nspontaneous magnetization in ferromagnets. Owing to the presence of the\nspin-orbit interaction the orbital and spin character of the Bloch states\ndepends sensitively on the orientation of the spins relative to the crystal\naxes. This leads to drastic changes in quantities which rely on interband\nmixing induced by the spin-orbit interaction. The anisotropy is particularly\nstriking for quantities which exhibit spiky and irregular distribution in the\nBrillouin zone, such as the spin-mixing parameter or the Berry curvature of the\nelectronic states. We demonstrate this for three cases: (i) the Elliott-Yafet\nspin-relaxation mechanism in paramagnets with structural inversion symmetry;\n(ii) the intrinsic anomalous Hall effect in ferromagnets; and (iii) the spin\nHall effect in paramagnets. We discuss the consequences of the pronounced\nanisotropic behavior displayed by these properties for spin-polarized transport\napplications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetotransport in multi-Weyl semimetals: A kinetic theory approach: We study the longitudinal magnetotransport in three-dimensional multi-Weyl\nsemimetals, constituted by a pair of (anti)-monopole of arbitrary integer\ncharge ($n$), with $n=1,2$ and $3$ in a crystalline environment. For any $n>1$,\neven though the distribution of the underlying Berry curvature is anisotropic,\nthe corresponding intrinsic component of the longitudinal magnetoconductivity\n(LMC), bearing the signature of the chiral anomaly, is insensitive to the\ndirection of the external magnetic field ($B$) and increases as $B^2$, at least\nwhen it is sufficiently weak (the semi-classical regime). In addition, the LMC\nscales as $n^3$ with the monopole charge. We demonstrate these outcomes for two\ndistinct scenarios, namely when inter-particle collisions in the Weyl medium\nare effectively described by (a) a single and (b) two (corresponding to inter-\nand intra-valley) scattering times. While in the former situation the\ncontribution to LMC from chiral anomaly is inseparable from the non-anomalous\nones, these two contributions are characterized by different time scales in the\nlater construction. Specifically for sufficiently large inter-valley scattering\ntime the LMC is dominated by the anomalous contribution, arising from the\nchiral anomaly. The predicted scaling of LMC and the signature of chiral\nanomaly can be observed in recently proposed candidate materials, accommodating\nmulti-Weyl semimetals in various solid state compounds.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Giant spin-orbit torque in a single ferrimagnetic metal layer: Antiferromagnets and compensated ferrimagnets offer opportunities to\ninvestigate spin dynamics in the 'terahertz gap' because their resonance modes\nlie in the 0.3 THz to 3 THz range. Despite some inherent advantages when\ncompared to ferromagnets, these materials have not been extensively studied due\nto difficulties in exciting and detecting the high-frequency spin dynamics,\nespecially in thin films. Here we show that spin-obit torque in a single layer\nof the highly spin-polarized compensated ferrimagnet Mn2RuxGa is remarkably\nefficient at generating spin-orbit fields \\mu_0H_eff, which approach 0.1x10-10\nT m2/A in the low-current density limit -- almost a thousand times the Oersted\nfield, and one to two orders of magnitude greater than the effective fields in\nheavy metal/ferromagnet bilayers. From an analysis of the harmonic Hall effect\nwhich takes account of the thermal contributions from the anomalous Nernst\neffect, we show that the antidamping component of the spin-orbit torque is\nsufficient to sustain self-oscillation. Our study demonstrates that spin\nelectronics has the potential to underpin energy-frugal, chip-based solutions\nto the problem of ultra high-speed information transfer.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Growth and Optical Properties Investigation of Pure and Al-doped SnO2\n  Nanostructures by Sol-Gel Method: SnO2 nanoparticles with different percentage of Al (5%, 15%, and25%) were\nsynthesized by sol-gel method. The structure and nature of nanoparticles are\ndetermined by of X-ray diffraction analysis. Also morphology of the samples is\nevaluated by SEM. Moreover, the optical properties of the samples are\ninvestigated with UV-Visible and FT-IR. The XRD patterns are indicated that all\nsamples and incorporation aluminum ions into the SnO2 lattice have tetragonal\nrutile structure. The crystalline size of nanoparticles is decreased with\nincreasing the Al percentage. The SEM results confirmed that the size of\nnanoparticles decreases with increasing the Al percentage. Also, FT-IR and\nUV-Visible results showed that the optical band gap of nanoparticles increases\nwith the increasing the Al percentage. Finally, we have used the EDX analysis\nto study the chemical composition of the products. Pure tin and oxygen have\nbeen observed. The doped samples showed the existence of Al atoms in the\nsamples of the crystal structure of SnO2.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Gate-induced magneto-oscillation phase anomalies in graphene bilayers: The magneto-oscillations in graphene bilayers are studied in the vicinity of\nthe K and K' points of the Brillouin zone within the four-band continuum model\nased on the simplest tight-binding approximation involving only the nearest\nneighbor interactions. The model is employed to construct Landau plots for a\nvariety of carrier concentrations and bias strengths between the graphene\nplanes. The quantum-mechanical and quasiclassical approaches are compared. We\nfound that the quantum magneto-oscillations are only asymptotically periodic\nand reach the frequencies predicted quasiclassically for high indices of Landau\nlevels. In unbiased bilayers the phase of oscillations is equal to the phase of\nmassive fermions. Anomalous behavior of oscillation phases was found in biased\nbilayers with broken inversion symmetry. The oscillation frequencies again tend\nto quasiclassically predicted ones, which are the same for $K$ and $K'$, but\nthe quantum approach yields the gate-tunable corrections to oscillation phases,\nwhich differ in sign for K and K'. These valley-dependent phase corrections\ngive rise, instead of a single quasiclassical series of oscillations, to two\nseries with the same frequency but shifted in phase.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nonabelian magnonics in antiferromagnets: We present a semiclassical formalism for antiferromagnetic (AFM) magnonics\nwhich promotes the central ingredient of spin wave chirality, encoded in a\nquantity called magnonic isospin, to a first-class citizen of the theory. We\nuse this formalism to unify results of interest from the field under a single\nchirality-centric formulation. Our main result is that the isospin is governed\nby unitary time evolution, through a Hamiltonian projected down from the full\nspin wave dynamics. Because isospin is SU(2)-valued, its dynamics on the Bloch\nsphere are precisely rotations - which, in general, do not commute.\nConsequently, the induced group of operations on AFM spin waves is nonabelian.\nThis is a paradigmatic departure from ferromagnetic magnonics, which operates\npurely within the abelian group generated by spin wave phase and amplitude. Our\ninvestigation of this nonabelian magnonics in AFM insulators focuses on\nstudying several simple gate operations, and offering in broad strokes a\nprogram of study for interesting new logic families in antiferromagnetic spin\nwave systems",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A Compact Approximate Solution to the Friedel-Anderson Impuriy Problem: An approximate groundstate of the Anderson-Friedel impurity problem is\npresented in a very compact form. It requires solely the optimization of two\nlocalized electron states and consists of four Slater states (Slater\ndeterminants). The resulting singlet ground state energy lies far below the\nAnderson mean field solution and agrees well with the numerical results by\nGunnarsson and Schoenhammer, who used an extensive 1/N_{f}-expansion for a spin\n1/2 impurity with double occupancy of the impurity level.\n  PACS: 85.20.Hr, 72.15.Rn",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coherent phonon Rabi oscillations with a high frequency carbon nanotube\n  phonon cavity: Phonon-cavity electromechanics allows the manipulation of mechanical\noscillations similar to photon-cavity systems. Many advances on this subject\nhave been achieved in various materials. In addition, the coherent phonon\ntransfer (phonon Rabi oscillations) between the phonon cavity mode and another\noscillation mode has attracted many interest in nano-science. Here we\ndemonstrate coherent phonon transfer in a carbon nanotube phonon-cavity system\nwith two mechanical modes exhibiting strong dynamical coupling. The\ngate-tunable phonon oscillation modes are manipulated and detected by extending\nthe red-detuned pump idea of photonic cavity electromechanics. The first- and\nsecond-order coherent phonon transfers are observed with Rabi frequencies 591\nkHz and 125 kHz, respectively. The frequency quality factor product\nfQ_m~2=10^12 Hz achieved here is larger thank k_B T_base/h, which may enable\nthe future realization of Rabi oscillations in the quantum regime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Decoherence of two entangled spin qubits coupled to an interacting\n  sparse nuclear spin bath: application to nitrogen vacancy centers: We consider pure dephasing of Bell states of electron spin qubits interacting\nwith a sparse bath of nuclear spins. Using the newly developed two-qubit\ngeneralization of cluster correlation expansion method, we calculate the spin\necho decay of $|\\Psi\\rangle$ and $|\\Phi\\rangle$ states for various interqubit\ndistances. Comparing the results with calculations in which dephasing of each\nqubit is treated independently, we identify signatures of influence of common\npart of the bath on the two qubits. At large interqubit distances, this common\npart consists of many nuclei weakly coupled to both qubits, so that decoherence\ncaused by it can be modeled by considering multiple uncorrelated sources of\nnoise (clusters of nuclei), each of them weakly affecting the qubits.\nConsequently, the resulting genuinely two-qubit contribution to decoherence can\nbe described as being caused by classical Gaussian noise. On the other hand,\nfor small interqubit distances the common part of the environment contains\nclusters of spins that are strongly coupled to both qubits, and their\ncontribution to two-qubit dephasing has visibly non-Gaussian character. We show\nthat one van easily obtain information about non-Gaussianity of environmental\nnoise affecting the qubits from the comparison of dephasing of $|\\Psi\\rangle$\nand $|\\Phi\\rangle$ Bell states. Numerical results are obtained for two nitrogen\nvacancy centers interacting with a bath of $^{13}$C nuclei of natural\nconcentration, for which we obtain that Gaussian description of correlated part\nof environmental noise starts to hold for centers separated by about 3 nm.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Zero-point fluctuations in the ground state of a mesoscopic normal ring: We investigate the persistent current of a ring with an in-line quantum dot\ncapacitively coupled to an external circuit. Of special interest is the\nmagnitude of the persistent current as a function of the external impedance in\nthe zero temperature limit when the only fluctuations in the external circuit\nare zero-point fluctuations. These are time-dependent fluctuations which\npolarize the ring-dot structure and we discuss in detail the contribution of\ndisplacement currents to the persistent current. We have earlier discussed an\nexact solution for the persistent current and its fluctuations based on a Bethe\nansatz. In this work, we emphasize a physically more intuitive approach using a\nLangevin description of the external circuit. This approach is limited to weak\ncoupling between the ring and the external circuit. We show that the zero\ntemperature persistent current obtained in this approach is consistent with the\npersistent current calculated from a Bethe ansatz solution. In the absence of\ncoupling our system is a two level system consisting of the ground state and\nthe first excited state. In the presence of coupling we investigate the\nprojection of the actual state on the ground state and the first exited state\nof the decoupled ring. With each of these projections we can associate a phase\ndiffusion time. In the zero temperature limit we find that the phase diffusion\ntime of the excited state projection saturates, whereas the phase diffusion\ntime of the ground state projection diverges.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Entanglement genesis by ancilla-based parity measurement in 2D circuit\n  QED: We present an indirect two-qubit parity meter in planar circuit quantum\nelectrodynamics, realized by discrete interaction with an ancilla and a\nsubsequent projective ancilla measurement with a dedicated, dispersively\ncoupled resonator. Quantum process tomography and successful entanglement by\nmeasurement demonstrate that the meter is intrinsically quantum non-demolition.\nSeparate interaction and measurement steps allow commencing subsequent data\nqubit operations in parallel with ancilla measurement, offering time savings\nover continuous schemes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Graphene Plasmonics: a Novel Fully Atomistic Approach for Realistic\n  Structures: We demonstrate that the plasmonic properties of realistic graphene and\ngraphene-based materials can effectively and accurately be modeled by a novel,\nfully atomistic, yet classical, approach, named $\\omega$FQ. Such model is able\nto reproduce all plasmonic features of these materials, and their dependence on\nshape, dimension and fundamental physical parameters (Fermi energy, relaxation\ntime and two-dimensional electron density). Remarkably, $\\omega$FQ is able to\naccurately reproduce experimental data for realistic structures of hundreds of\nnanometers ($\\sim$ 370.000 atoms), which cannot be afforded by any\n\\emph{ab-initio} method. Also, the atomistic nature of $\\omega$FQ permits the\ninvestigation of complex shapes, which can hardly be dealt with by exploiting\nwidespread continuum approaches.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-Orbit Based Coherent Spin Ratchets: The concept of ratchets, driven asymmetric periodic structures giving rise to\ndirected particle flow, has recently been generalized to a quantum ratchet\nmechanism for spin currents mediated through spin-orbit interaction. Here we\nconsider such systems in the coherent mesoscopic regime and generalize the\nproposal of a minimal spin ratchet model based on a non-interacting clean\nquantum wire with two transverse channels by including disorder and by\nself-consistently treating the charge redistribution in the nonlinear\n(adiabatic) ac-driving regime. Our Keldysh-Green function based quantum\ntransport simulations show that the spin ratchet mechanism is robust and\nprevails for disordered, though non-diffusive, mesoscopic structures. Extending\nthe two-channel to the multi-channel case does not increase the net ratchet\nspin current efficiency but, remarkably, yields a dc spin transmission\nincreasing linearly with channel number.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Decoherence in qubits due to low-frequency noise: The efficiency of the future devices for quantum information processing is\nlimited mostly by the finite decoherence rates of the qubits. Recently a\nsubstantial progress was achieved in enhancing the time, which a solid-state\nqubit demonstrates a coherent dynamics. This progress is based mostly on a\nsuccessful isolation of the qubits from external decoherence sources. Under\nthese conditions the material-inherent sources of noise start to play a crucial\nrole. In most cases the noise that quantum device demonstrate has 1/f spectrum.\nThis suggests that the environment that destroys the phase coherence of the\nqubit can be thought of as a system of two-state fluctuators, which experience\nrandom hops between their states. In this short review we discuss the current\nstate of the theory of the decoherence due to the qubit interaction with the\nfluctuators. We describe the effect of such an environment on different\nprotocols of the qubit manipulations - free induction and echo signal. It turns\nout that in many important cases the noise produced by the fluctuators is\nnon-Gaussian. Consequently the results of the interaction of the qubit with the\nfluctuators are not determined by the pair correlation function only.\n  We describe the effect of the fluctuators using so-called spin-fluctuator\nmodel. Being quite realistic this model allows one to evaluate the qubit\ndynamics in the presence of one fluctuator exactly. This solution is found, and\nits features, including non-Gaussian effects are analyzed in details. We extend\nthis consideration for the systems of large number of fluctuators, which\ninteract with the qubit and lead to the 1/f noise. We discuss existing\nexperiments on the Josephson qubit manipulation and try to identify\nnon-Gaussian behavior.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Perspective on Coupled Colloidal Quantum Dot Molecules: Electronic coupling and hence hybridization of atoms serve as the basis for\nthe rich properties of the endless library of naturally occurring molecules.\nColloidal quantum dots (CQDs) manifesting quantum strong confinement, possess\natomic like characteristics with s and p electronic levels, which popularized\nthe notion of CQDs as artificial atoms. Continuing this analogy, when two atoms\nare close enough to form a molecule so that their orbitals start overlapping,\nthe orbitals' energies start to split into bonding and anti-bonding states made\nout of hybridized orbitals. The same concept is also applicable for two fused\ncore-shell nanocrystals in close proximity. Their band-edge states, which\ndictate the emitted photon energy, start to hybridize changing their electronic\nand optical properties. Thus, an exciting direction of artificial molecules\nemerges leading to a multitude of possibilities for creating a library of new\nhybrid nanostructures with novel optoelectronic properties with relevance\ntowards diverse applications including quantum technologies. In a model fused\ncore-shell homodimer molecule, the hybridization energy is strongly correlated\nwith the extent of structural continuity, the delocalization of the exciton\nwavefunction, and the barrier thickness as calculated numerically. The\nhybridization impacts the emitted photon statistics manifesting a faster\nradiative decay rate, photon bunching effect, and modified Auger recombination\npathway compared to the monomer artificial atoms. Future perspectives for the\nnanocrystals chemistry paradigm are highlighted.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Coherence at Low Temperatures in Mesoscopic Systems: Effect of\n  Disorder: We study the disorder dependence of the phase coherence time of quasi\none-dimensional wires and two-dimensional (2D) Hall bars fabricated from a high\nmobility GaAs/AlGaAs heterostructure. Using an original ion implantation\ntechnique, we can tune the intrinsic disorder felt by the 2D electron gas and\ncontinuously vary the system from the semi-ballistic regime to the localized\none. In the diffusive regime, the phase coherence time follows a power law as a\nfunction of diffusion coefficient as expected in the Fermi liquid theory,\nwithout any sign of low temperature saturation. Surprisingly, in the\nsemi-ballistic regime, it becomes independent of the diffusion coefficient. In\nthe strongly localized regime we find a diverging phase coherence time with\ndecreasing temperature, however, with a smaller exponent compared to the weakly\nlocalized regime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quasi-Periodic Nanoripples in Graphene Grown by Chemical Vapor\n  Deposition and Its Impact on Charge Transport: The technical breakthrough in synthesizing graphene by chemical vapor\ndeposition methods (CVD) has opened up enormous opportunities for large-scale\ndevice applications. In order to improve the electrical properties of CVD\ngraphene grown on copper (Cu-CVD graphene), recent efforts have focussed on\nincreasing the grain size of such polycrystalline graphene films to 100\nmicrometers and larger. While an increase in grain size and hence, a decrease\nof grain boundary density is expected to greatly enhance the device\nperformance, here we show that the charge mobility and sheet resistance of\nCu-CVD graphene is already limited within a single grain. We find that the\ncurrent high-temperature growth and wet transfer methods of CVD graphene result\nin quasi-periodic nanoripple arrays (NRAs). Electron-flexural phonon scattering\nin such partially suspended graphene devices introduces anisotropic charge\ntransport and sets limits to both the highest possible charge mobility and\nlowest possible sheet resistance values. Our findings provide guidance for\nfurther improving the CVD graphene growth and transfer process.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Numerical Analysis of the Anderson Localization: The aim of this paper is to demonstrate, by simple numerical simulations, the\nmain transport properties of disordered electron systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Phenomena in Low-Dimensional Systems: A brief summary of the physics of low-dimensional quantum systems is given.\nThe material should be accessible to advanced physics undergraduate students.\nReferences to recent review articles and books are provided when possible.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Observation of charged excitons in hole-doped carbon nanotubes using\n  photoluminescence and absorption spectroscopy: We report the first observation of trions (charged excitons), three-particle\nbound states consisting of one electron and two holes, in hole-doped carbon\nnanotubes at room temperature. When p-type dopants are added to carbon nanotube\nsolutions, the photoluminescence and absorption peaks of the trions appear far\nbelow the E11 bright exciton peak, regardless of the dopant species. The\nunexpectedly large energy separation between the bright excitons and the trions\nis attributed to the strong electron-hole exchange interaction in carbon\nnanotubes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Giant Interaction-Induced Gap and Electronic Phases in Rhombohedral\n  Trilayer Graphene: Due to their unique electron dispersion and lack of a Fermi surface, Coulomb\ninteractions in undoped two-dimensional Dirac systems, such as single, bi- and\ntri-layer graphene, can be marginal or relevant. Relevant interactions can\nresult in spontaneous symmetry breaking, which is responsible for a large class\nof physical phenomena ranging from mass generation in high energy physics to\ncorrelated states such as superconductivity and magnetism in condensed matter.\nHere, using transport measurements, we show that rhombohedral-stacked trilayer\ngraphene (r-TLG) offers a simple, yet novel and tunable, platform for study of\nvarious phases with spontaneous or field-induced broken symmetries. Here, we\nshow that, contrary to predictions by tight-binding calculations,\nrhombohedral-stacked trilayer graphene (r-TLG) is an intrinsic insulator, with\na giant interaction-induced gap {\\Delta}~42meV. This insulating state is a\nspontaneous layer antiferromagnetic with broken time reversal symmetry, and can\nbe suppressed by increasing charge density n, an interlayer potential, a\nparallel magnetic field, or a critical temperature Tc~38K. This gapped\ncollective state can be explored for switches with low input power and high\non/off ratio.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Hall system in Tao-Thouless limit: We consider spin-polarized electrons in a single Landau level on a torus. The\nquantum Hall problem is mapped onto a one-dimensional lattice model with\nlattice constant $2\\pi/L_1$, where $L_1$ is a circumference of the torus (in\nunits of the magnetic length). In the Tao-Thouless limit, $L_1\\to 0$, the\ninteracting many-electron problem is exactly diagonalized at any rational\nfilling factor $\\nu=p/q\\le 1$. For odd $q$, the ground state has the same\nqualitative properties as a bulk ($L_1 \\to \\infty$) quantum Hall hierarchy\nstate and the lowest energy quasiparticle exitations have the same fractional\ncharges as in the bulk. These states are the $L_1 \\to 0$ limits of the\nLaughlin/Jain wave functions for filling fractions where these exist. We argue\nthat the exact solutions generically, for odd $q$, are continuously connected\nto the two-dimensional bulk quantum Hall hierarchy states, {\\it ie} that there\nis no phase transition as $L_1 \\to \\infty$ for filling factors where such\nstates can be observed. For even denominator fractions, a phase transition\noccurs as $L_1$ increases. For $\\nu=1/2$ this leads to the system being mapped\nonto a Luttinger liquid of neutral particles at small but finite $L_1$, this\nthen develops continuously into the composite fermion wave function that is\nbelieved to describe the bulk $\\nu=1/2$ system. The analysis generalizes to\nnon-abelian quantum Hall states.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum manipulation in a Josephson LED: We access the suitability of the recently proposed Josephson LED for quantum\nmanipulation purposes. We show that the device can both be used for on-demand\nproduction of entangled photon pairs and operated as a two-qubit gate. Besides,\none can entangle particle spin with photon polarization and/or measure the spin\nby measuring the polarization.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Model for Topological Phononics and Phonon Diode: The quantum anomalous Hall effect, an exotic topological state first\ntheoretically predicted by Haldane and recently experimentally observed, has\nattracted enormous interest for low-power-consumption electronics. In this\nwork, we derived a Schr{\\\"o}dinger-like equation of phonons, where\ntopology-related quantities, time reversal symmetry and its breaking can be\nnaturally introduced similar as for electrons. Furthermore, we proposed a\nphononic analog of the Haldane model, which gives the novel quantum (anomalous)\nHall-like phonon states characterized by one-way gapless edge modes immune to\nscattering. The topologically nontrivial phonon states are useful not only for\nconducting phonons without dissipation but also for designing highly efficient\nphononic devices, like an ideal phonon diode, which could find important\napplications in future phononics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Scaling of intrinsic domain wall magneto-resistance with confinement in\n  electromigrated nanocontacts: In this work we study the evolution of intrinsic domain wall\nmagnetoresistance (DWMR) with domain wall confinement. Clean permalloy notched\nhalf-ring nanocontacts are fabricated using a special ultra-high vacuum\nelectromigration procedure to tailor the size of the wire in-situ and through\nthe resulting domain wall confinement we tailor the domain wall width from a\nfew tens of nm down to a few nm. Through measurements of the dependence of the\nresistance with respect to the applied field direction we extract the\ncontribution of a single domain wall to the MR of the device, as a function of\nthe domain wall width in the confining potential at the notch. In this size\nrange, an intrinsic positive MR is found, which dominates over anisotropic MR,\nas confirmed by comparison to micromagnetic simulations. Moreover, the MR is\nfound to scale monotonically with the size of the domain wall, $\\delta_{DW}$,\nas 1/$\\delta_{DW}^b$, with $b=2.31\\pm 0.39 $. The experimental result is\nsupported by quantum-mechanical transport simulations based on ab-initio\ndensity functional theory calculations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Plasmons enhance near-field radiative heat transfer for graphene-covered\n  dielectrics: It is shown that a graphene layer on top of a dielectric slab can\ndramatically influence the ability of this dielectric for radiative heat\nexchange. Effect of graphene is related to thermally excited plasmons.\nFrequency of these resonances lies in the terahertz region and can be tuned by\nvarying the Fermi level through doping or gating. Heat transfer between two\ndielectrics covered with graphene can be larger than that between best known\nmaterials and even much larger at low temperatures. Moreover, high heat\ntransfer can be significantly modulated by electrical means that opens up new\npossibilities for very fast manipulations with the heat flux.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Exciton Polaritons in a Two-Dimensional Lieb Lattice with Spin-Orbit\n  Coupling: We study exciton-polaritons in a two-dimensional Lieb lattice of\nmicropillars. The energy spectrum of the system features two flat bands formed\nfrom $S$ and $P_{x,y}$ photonic orbitals, into which we trigger bosonic\ncondensation under high power excitation. The symmetry of the orbital wave\nfunctions combined with photonic spin-orbit coupling gives rise to emission\npatterns with pseudospin texture in the flat band condensates. Our work shows\nthe potential of polariton lattices for emulating flat band Hamiltonians with\nspin-orbit coupling, orbital degrees of freedom and interactions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum thermodynamics in a single-electron box: This chapter provides an overview of the methods and results for quantum\nthermodynamic experiments with single-electron devices. The experiments with a\nsingle-electron box on Jarzynski equality and Crooks relation, two-temperature\nfluctuation relations, and Maxwell's demon performed over the past few years\nare reviewed here. We further review the first experimental realization of an\nautonomous Maxwell's demon using a single-electron box as the demon.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "$\u0393(2)$ modular symmetry, renormalization, group flow and the\n  quantum Hall effect: We construct a family of holomorphic $\\beta$-functions whose RG flow\npreserves the $\\Gamma(2)$ modular symmetry and reproduces the observed\nstability of the Hall plateaus. The semi-circle law relating the longitudinal\nand Hall conductivities that has been observed experimentally is obtained from\nthe integration of the RG equations for any permitted transition which can be\nidentified from the selection rules encoded in the flow diagram. The generic\nscale dependance of the conductivities is found to agree qualitatively with the\npresent experimental data. The existence of a crossing point occuring in the\ncrossover of the permitted transitions is discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Origin of Discrepancies in Inelastic Electron Tunneling Spectra of\n  Molecular Junctions: We report inelastic electron tunneling spectroscopy (IETS) of multilayer\nmolecular junctions with and without incorporated metal nano-particles. The\nincorporation of metal nanoparticles into our devices leads to enhanced IET\nintensity and a modified line-shape for some vibrational modes. The enhancement\nand line-shape modification are both the result of a low lying hybrid metal\nnanoparticle-molecule electronic level. These observations explain the apparent\ndiscrepancy between earlier IETS measurements of alkane thiolate junctions by\nKushmerick \\emph{et al.} [Nano Lett. \\textbf{4}, 639 (2004)] and Wang \\emph{et\nal.} [Nano Lett. \\textbf{4}, 643 (2004)].",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Influence of MgO tunnel barrier thickness on spin-transfer ferromagnetic\n  resonance and torque in magnetic tunnel junctions: Spin-transfer ferromagnetic resonance (ST-FMR) in symmetric magnetic tunnel\njunctions (MTJs) with a varied thickness of the MgO tunnel barrier (0.75 nm <\n$t_{MgO}$ < 1.05 nm) is studied using the spin-torque diode effect. The\napplication of an RF current into nanosized MTJs generates a DC mixing voltage\nacross the device when the frequency is in resonance with the resistance\noscillations arising from the spin transfer torque. Magnetization precession in\nthe free and reference layers of the MTJs is analyzed by comparing ST-FMR\nsignals with macrospin and micromagnetic simulations. From ST-FMR spectra at\ndifferent DC bias voltage, the in-plane and perpendicular torkances are\nderived. The experiments and free-electron model calculations show that the\nabsolute torque values are independent of tunnel barrier thickness. The\ninfluence of coupling between the free and reference layer of the MTJs on the\nST-FMR signals and the derived torkances are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hole Flying Qubits in Quantum Dot Arrays: Quantum information transfer is fundamental for scalable quantum computing in\nany potential platform and architecture. Hole spin qubits, owing to their\nintrinsic spin-orbit interaction (SOI), promise fast quantum operations which\nare fundamental for the implementation of quantum gates. Yet, the influence of\nSOI in quantum transfer protocols remains an open question. Here, we\ninvestigate hole flying qubits using shortcuts to adiabaticity protocols, i.e.,\nthe long-range transfer of hole spin states and the quantum distribution of\nentangled pairs in semiconductor quantum dot arrays. We show that electric\nfield manipulation allows dynamical control of the SOI, enabling simultaneously\nthe implementation of quantum gates during the transfer, with the potential to\nsignificantly accelerate quantum algorithms. By harnessing the ability to\nperform quantum gates in parallel with the transfer, we employ dynamical\ndecoupling schemes to focus and preserve the spin state, leading to higher\ntransfer fidelity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunable microwave impedance matching to a high impedance source using a\n  Josephson metamaterial: We report the efficient coupling of a $50\\,\\Omega$ microwave circuit to a\nhigh impedance conductor. We use an impedance transformer consisting of a\n$\\lambda/4$ co-planar resonator whose inner conductor contains an array of\nsuperconducting quantum interference devices (SQUIDs), providing the resonator\nwith a large and tunable lineic inductance $\\mathcal{L}\\sim 80 \\mu_0$,\nresulting in a large characteristic impedance $Z_C\\sim 1\\,\\mathrm{k}\\Omega$.\nThe impedance matching efficiency is characterized by measuring the shot noise\npower emitted by a dc biased high resistance tunnel junction connected to the\nresonator. We demonstrate matching to impedances in the $15$ to\n$35\\,\\mathrm{k}\\Omega$ range with bandwidths above $100\\,\\mathrm{MHz}$ around a\nresonant frequency tunable in the $4$ to $6\\,\\mathrm{GHz}$ range.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Elementary Charge Transfer Processes in Mesoscopic Conductors: We determine charge transfer statistics in a quantum conductor driven by a\ntime-dependent voltage and identify the elementary transport processes. At zero\ntemperature unidirectional and bidirectional single charge transfers occur. The\nunidirectional processes involve electrons injected from the source terminal\ndue to excess dc bias voltage. The bidirectional processes involve\nelectron-hole pairs created by time-dependent voltage bias. This interpretation\nis further supported by the charge transfer statistics in a multiterminal beam\nsplitter geometry in which injected electrons and holes can be partitioned into\ndifferent outgoing terminals. The probabilities of elementary processes can be\nprobed by noise measurements: the unidirectional processes set the dc noise\nlevel while bidirectional ones give rise to the excess noise. For ac voltage\ndrive, the noise oscillates with increasing the driving amplitude. The\ndecomposition of the noise into the contributions of elementary processes\nidentifies the origin of these oscillations: the number of electron-hole pairs\ngenerated per cycle increases with increasing the amplitude. The decomposition\nof the noise into elementary processes is studied for different time-dependent\nvoltages. The method we use is also suitable for systematic calculation of\nhigher-order current correlators at finite temperature. We obtain current noise\npower and the third cumulant in the presence of time-dependent voltage drive.\nThe charge transfer statistics at finite temperature can be interpreted in\nterms of multiple charge transfers with probabilities which depend on energy\nand temperature.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous zero-temperature magnetopolaronic blockade of resonant\n  electron tunneling in Majorana-resonant-level single-electron transistor: The magnetopolaronic generalization of a Majorana-resonant-level (MRL) model\nis considered for a single-level vibrating quantum dot coupled to two\nhalf-infinite $g=1/2$ Tomonaga-Luttinger liquid (TLL) leads. A qualitatively\nnew non-trivial formula for the effective transmission coefficient and\ndifferential conductance for resonant magnetopolaron-assisted tunneling is\nobtained under the assumption about a fermion-boson factorization of\ncorresponding averages. This approach is valid for the case of weak\nmagnetopolaronic coupling in a system. Surprisingly, it is found that despite a\nsupposed weakness of interaction between fermionic and bosonic subsystems in\nthat case, a strongly correlated electron transport in the system reveals\nfeatures of strong (and, hence, anomalous) magnetopolaronic blockade at zero\ntemperature if the energy of a vibrational quantum is the smallest (but\nnonzero) energy parameter in the system. Such an effect should be referred to\nas magnetic phase-coherent magnetopolaron-assisted resonant tunneling of\nAndreev type, that originates from a special, Majorana-like, symmetry of\nmagnetopolaron-coupled tunnel Hamiltonian. The effect predicted in this paper\ncan be used as an experimental fingerprint of Majorana-resonant level situation\nin single-electron transistors as well as for detection of ultra-slow\nzero-point oscillations of suspended carbon nanotubes in the Majorana-resonant\nlevel regime of electron tunneling through corresponding single-electron\ntransistors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Alternating currents and shear waves in viscous electronics: Strong interaction among charge carriers can make them move like viscous\nfluid. Here we explore alternating current (AC) effects in viscous electronics.\nIn the Ohmic case, incompressible current distribution in a sample adjusts fast\nto a time-dependent voltage on the electrodes, while in the viscous case,\nmomentum diffusion makes for retardation and for the possibility of propagating\nslow shear waves. We focus on specific geometries that showcase interesting\naspects of such waves: current parallel to a one-dimensional defect and current\napplied across a long strip. We find that the phase velocity of the wave\npropagating along the strip respectively increases/decreases with the frequency\nfor no-slip/no-stress boundary conditions. This is so because when the\nfrequency or strip width goes to zero (alternatively, viscosity go to\ninfinity), the wavelength of the current pattern tends to infinity in the\nno-stress case and to a finite value in a general case. We also show that for\nDC current across a strip with no-stress boundary, there only one pair of\nvortices, while there is an infinite vortex chain for all other types of\nboundary conditions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cyclotron Resonance Assisted Photocurrents in Surface States of a 3D\n  Topological Insulator Based on a Strained High Mobility HgTe Film: We report on the observation of cyclotron resonance induced photocurrents,\nexcited by continuous wave terahertz radiation, in a 3D topological insulator\n(TI) based on an 80 nm strained HgTe film. The analysis of the photocurrent\nformation is supported by complimentary measurements of magneto-transport and\nradiation transmission. We demonstrate that the photocurrent is generated in\nthe topologically protected surface states. Studying the resonance response in\na gated sample we examined the behavior of the photocurrent, which enables us\nto extract the mobility and the cyclotron mass as a function of the Fermi\nenergy. For high gate voltages we also detected cyclotron resonance (CR) of\nbulk carriers, with a mass about two times larger than that obtained for the\nsurface states. The origin of the CR assisted photocurrent is discussed in\nterms of asymmetric scattering of TI surface carriers in the momentum space.\nFurthermore, we show that studying the photocurrent in gated samples provides a\nsensitive method to probe the effective masses and the mobility of 2D Dirac\nsurface states, when the Fermi level lies in the bulk energy gap or even in the\nconduction band.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dirac Theory and Topological Phases of Silicon Nanotube: Silicon nanotube is constructed by rolling up a silicene, i.e., a monolayer\nof silicon atoms forming a two-dimensional honeycomb lattice. It is a\nsemiconductor or an insulator owing to relatively large spin-orbit interactions\ninduced by its buckled structure. The key observation is that this buckled\nstructure allows us to control the band structure by applying electric field\n$E_z$. When $E_z$ is larger than a certain critical value $E_{\\text{cr}}$, by\nanalyzing the band structure and also on the basis of the effective Dirac\ntheory, we demonstrate the emergence of four helical zero-energy modes\npropagating along nanotube. Accordingly, a silicon nanotube contains three\nregions, namely, a topological insulator, a band insulator and a metallic\nregion separating these two types of insulators. The wave function of each zero\nmode is localized within the metallic region, which may be used as a quantum\nwire to transport spin currents in future spintronics. We present an analytic\nexpression of the wave function for each helical zero mode. These results are\napplicable also to germanium nanotube.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Experimental demonstrations of high-Q superconducting coplanar waveguide\n  resonators: We designed and successfully fabricated an absorption-type of superconducting\ncoplanar waveguide (CPW) resonators. The resonators are made from a Niobium\nfilm (about 160 nm thick) on a high-resistance Si substrate, and each resonator\nis fabricated as a meandered quarter-wavelength transmission line (one end\nshorts to the ground and another end is capacitively coupled to a through\nfeedline). With a vector network analyzer we measured the transmissions of the\napplied microwave through the resonators at ultra-low temperature (e.g., at 20\nmK), and found that their loaded quality factors are significantly high, i.e.,\nup to 10^6. With the temperature increases slowly from the base temperature\n(i.e., 20 mK), we observed the resonance frequencies of the resonators are blue\nshifted and the quality factors are lowered slightly. In principle, this type\nof CPW-device can integrate a series of resonators with a common feedline,\nmaking it a promising candidate of either the data bus for coupling the distant\nsolid-state qubits or the sensitive detector of single photons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nano-ironing van der Waals Heterostructures Towards Electrically\n  Controlled Quantum Dots: Assembling two-dimensional van der Waals layered materials into\nheterostructures is an exciting development that sparked the discovery of rich\ncorrelated electronic phenomena and offers possibilities for designer device\napplications. However, resist residue from fabrication processes is a major\nlimitation. Resulting disordered interfaces degrade device performance and mask\nunderlying transport physics. Conventional cleaning processes are inefficient\nand can cause material and device damage. Here, we show that thermal scanning\nprobe based cleaning can effectively eliminate resist residue to recover\npristine material surfaces. Our technique is compatible at both the material-\nand device-level, and we demonstrate the significant improvement in the\nelectrical performance of 2D WS2 transistors. We also demonstrate the cleaning\nof van der Waals heterostructures to achieve interfaces with low disorder. This\nenables the electrical formation and control of quantum dots that can be tuned\nfrom macroscopic current flow to the single-electron tunnelling regime. Such\nmaterial processing advances are crucial for constructing high-quality vdW\nheterostructures that are important platforms for fundamental studies and\nbuilding blocks for quantum and nano-electronics applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Operation of graphene quantum Hall resistance standard in a cryogen-free\n  table-top system: We demonstrate quantum Hall resistance measurements with metrological\naccuracy in a small cryogen-free system operating at a temperature of around\n3.8K and magnetic fields below 5T. Operating this system requires little\nexperimental knowledge or laboratory infrastructure, thereby greatly advancing\nthe proliferation of primary quantum standards for precision electrical\nmetrology. This significant advance in technology has come about as a result of\nthe unique properties of epitaxial graphene on SiC.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "High thermoelectric performance in excitonic bilayer graphene: We consider the excitonic effects on the thermal properties in the AB-stacked\nbilayer graphene. The calculations are based on the bilayer generalization of\nthe usual Hubbard model at the half-filling. The full interaction bandwidth is\nused without any low-energy assumption. We obtain the unusually high values for\nthe electronic figure of merit even at the room-temperatures which is very\npromising for the thermoelectric applications of the AB-bilayer structure. We\ndiscuss the effects of the interlayer Coulomb interaction and temperature on\ndifferent thermal parameters in the bilayer graphene and we emphasize the role\nof the charge neutrality point in the thermal properties and within the\nexcitonic insulator transition scenario. The calculated values of the rate of\nthermoelectric conversion efficiency suggest the possibility of\nhigh-performance device applications of AB-bilayer graphene.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Exotic plasma as classical Hall Liquid: A non-relativistic plasma model endowed with an ``exotic'' structure\nassociated with the two-parameter central extension of the planar Galilei group\nis constructed. Introducing a Chern-Simons statistical gauge field provides us\nwith a self-consistent system; when the magnetic field takes a critical value\ndetermined by the extension parameters, the fluid becomes incompressible and\nmoves collectively, according to the Hall law.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Majorana edge modes of topological exciton condensate with\n  superconductors: I study the edge states of the topological exciton condensate formed by\nCoulomb interaction between two parallel surfaces of a strong topological\ninsulator. When the condensate is contacted by superconductors with a {\\pi}\nphase shift across the two surfaces, a pair of counter-propagating Majorana\nmodes close the gap at the boundary. I propose a nano-structured system of\ntopological insulators and superconductors to realize unpaired Majorana\nfermions. The Majorana signal can be used to detect the formation of the\ntopological exciton condensate. The relevant experimental signatures as well as\nimplications for related systems are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Sign changes and resonance of intrinsic spin Hall effect in\n  two-dimensional hole gas: The intrinsic spin Hall conductance shows rich sign changes by applying a\nperpendicular magnetic field in a two-dimensional hole gas. Especially, a\nnotable sign changes can be achieved by adjusting the characteristic length of\nthe Rashba coupling and hole density at moderate magnetic fields. This sign\nissue may be easily realized in experiments. The oscillations of the intrinsic\nspin Hall conductance as a function of 1/$B$ is nothing else but Shubnikov-de\nHaas oscillations, and the additional beatings can be quantitatively related to\nthe value of the spin-orbit coupling parameter. The Zeeman splitting is too\nsmall to introduce effective degeneracy between different Landau levels in a\ntwo-dimensional hole gas, and the resonant intrinsic spin Hall conductance\nappears in high hole density and strong magnetic field due to the transition\nbetween mostly spin-$-{1/2}$ holes and spin-3/2 holes is confirmed. Two likely\nways to establish intrinsic spin Hall effect in experiments and a possible\napplication are suggested.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ripples in a graphene membrane coupled to Glauber spins: We propose a theory of ripples in suspended graphene sheets based on\ntwo-dimensional elasticity equations that are made discrete on the honeycomb\nlattice and then periodized. At each point carbon atoms are coupled to Ising\nspins whose values indicate the atoms local trend to move vertically off-plane.\nThe Ising spins are in contact with a thermal bath and evolve according to\nGlauber dynamics. In the limit of slow spin flip compared to membrane\nvibrations, ripples with no preferred orientation appear as long-lived\nmetastable states for any temperature. Numerical solutions confirm this\npicture.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electric generation of spin in crystals with reduced symmetry: We propose a simple way of evaluating the bulk spin generation of an\narbitrary crystal with a known band structure in the strong spin-orbit coupling\nlimit. We show that, in the presence of an electric field, there exists an\nintrinsic torque term which gives rise to a nonzero spin generation rate. Using\nmethods similar to those of recent experiments which measure spin polarization\nin semiconductors, this spin generation rate should be experimentally\nobservable. The wide applicability of this effect is emphasized by explicit\nconsideration of a range of examples: bulk wurtzite and strained zincblende\n(n-GaAs) lattices, as well as quantum well heterojunction systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Designer quantum states of matter created atom-by-atom: With the advances in high resolution and spin-resolved scanning tunneling\nmicroscopy as well as atomic-scale manipulation, it has become possible to\ncreate and characterize quantum states of matter bottom-up, atom-by-atom. This\nis largely based on controlling the particle- or wave-like nature of electrons,\nas well as the interactions between spins, electrons, and orbitals and their\ninterplay with structure and dimensionality. We review the recent advances in\ncreating artificial electronic and spin lattices that lead to various exotic\nquantum phases of matter, ranging from topological Dirac dispersion to complex\nmagnetic order. We also project future perspectives in non-equilibrium\ndynamics, prototype technologies, engineered quantum phase transitions and\ntopology, as well as the evolution of complexity from simplicity in this newly\ndeveloping field.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Energy Spectrum and Quantum Hall Effect in Twisted Bilayer Graphene: We investigate the electronic spectra and quantum Hall effect in twisted\nbilayer graphenes with various rotation angles under magnetic fields, using a\nmodel rigorously including the interlayer interaction. We describe the spectral\nevolution from discrete Landau levels in the weak field regime to the fractal\nband structure in the strong field regime, and estimate the quantized Hall\nconductivity for each single gap. In weak magnetic fields, the low-energy\nconduction band of the twisted bilayer is quantized into electron-like Landau\nlevels and hole-like Landau levels above and below the van Hove singularity,\nrespectively, reflecting a topological change of the Fermi surface between\nelectron pocket and hole pocket. Accordingly the Hall conductivity exhibits a\nsharp drop from positive to negative at the transition point. In increasing\nmagnetic field, the spectrum gradually evolves into fractal band structure\nso-called Hofstadter's butterfly, where the Hall conductivity exhibits a\nnonmonotonic behavior varying from a minigap to a minigap. The magnetic field\nstrength required to invoke the fractal band structure is more feasible in\nsmaller rotating angle.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Localization of Two Interacting Particles in One-Dimensional Random\n  Potential: We investigate the localization of two interacting particles in\none-dimensional random potential. Our definition of the two-particle\nlocalization length, $\\xi$, is the same as that of v. Oppen et al. [Phys. Rev.\nLett. 76, 491 (1996)] and $\\xi$'s for chains of finite lengths are calculated\nnumerically using the recursive Green's function method for several values of\nthe strength of the disorder, $W$, and the strength of interaction, $U$. When\nU=0, $\\xi$ approaches a value larger than half the single-particle localization\nlength as the system size tends to infinity and behaves as $\\xi \\sim\nW^{-\\nu_0}$ for small $W$ with $\\nu_0 = 2.1 \\pm 0.1$. When $U\\neq 0$, we use\nthe finite size scaling ansatz and find the relation $\\xi \\sim W^{-\\nu}$ with\n$\\nu = 2.9 \\pm 0.2$. Moreover, data show the scaling behavior $\\xi \\sim\nW^{-\\nu_0} g(|U|/W^\\Delta)$ with $\\Delta = 4.0 \\pm 0.5$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Floquet engineering of lattice structure and dimensionality in twisted\n  moir\u00e9 heterobilayers: We present an experimental proposal to tune the effective lattice structure\nin twisted transition metal dichalcogenide (TMD) heterobilayers with\ntime-periodic Floquet drive. We show that elliptically polarized light with\nsub-terahertz frequencies $\\hbar\\omega\\sim 1$ meV and moderate electric fields\n$E\\sim0.2$~MV/cm allows tuning between the native triangular lattice and a\nsquare lattice, while linearly polarized light enables dimensional reduction to\na quasi-one-dimensional geometry. Without drive, these twisted TMDs simulate\nthe single band Fermi-Hubbard model; we show that this approximation still\nholds in the presence of drive. This control opens the door to explore a rich\nvariety of correlated phases of matter, such as spin liquids and d-wave\nsuperconductivity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Signatures of Majorana fermions in hybrid superconductor-semiconductor\n  nanowire devices: Majorana fermions are particles identical to their own antiparticles. They\nhave been theoretically predicted to exist in topological superconductors. We\nreport electrical measurements on InSb nanowires contacted with one normal (Au)\nand one superconducting electrode (NbTiN). Gate voltages vary electron density\nand define a tunnel barrier between normal and superconducting contacts. In the\npresence of magnetic fields of order 100 mT we observe bound, mid-gap states at\nzero bias voltage. These bound states remain fixed to zero bias even when\nmagnetic fields and gate voltages are changed over considerable ranges. Our\nobservations support the hypothesis of Majorana fermions in nanowires coupled\nto superconductors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin dynamics in InAs-nanowire quantum-dots coupled to a transmission\n  line: We study theoretically electron spins in nanowire quantum dots placed inside\na transmission line resonator. Because of the spin-orbit interaction, the spins\ncouple to the electric component of the resonator electromagnetic field and\nenable coherent manipulation, storage, and read-out of quantum information in\nan all-electrical fashion. Coupling between distant quantum-dot spins, in one\nand the same or different nanowires, can be efficiently performed via the\nresonator mode either in real time or through virtual processes. For the latter\ncase we derive an effective spin-entangling interaction and suggest means to\nturn it on and off. We consider both transverse and longitudinal types of\nnanowire quantum-dots and compare their manipulation timescales against the\nspin relaxation times. For this, we evaluate the rates for spin relaxation\ninduced by the nanowire vibrations (phonons) and show that, as a result of\nphonon confinement in the nanowire, this rate is a strongly varying function of\nthe spin operation frequency and thus can be drastically reduced compared to\nlateral quantum dots in GaAs. Our scheme is a step forward to the formation of\nhybrid structures where qubits of different nature can be integrated in a\nsingle device.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin superfluidity and long-range transport in thin-film ferromagnets: In ferromagnets, magnons may condense into a single quantum state. Analogous\nto superconductors, this quantum state may support transport without\ndissipation. Recent works suggest that longitudinal spin transport through a\nthin-film ferromagnet is an example of spin superfluidity. Although intriguing,\nthis tantalizing picture ignores long-range dipole interactions; we demonstrate\nthat such interactions dramatically affect spin transport. In single-film\nferromagnets, \"spin superfluidity\" only exists at length scales (a few hundred\nnanometers in yttrium iron garnet) somewhat larger than the exchange length.\nOver longer distances, dipolar interactions destroy spin superfluidity.\nNevertheless, we predict re-emergence of spin superfluidity in tri-layer\nferromagnet--normal metal--ferromagnet films of $\\sim 1\\, \\mu$m in size. Such\nsystems also exhibit other types of long-range spin transport in samples\nseveral micrometers in size.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Gate-control of spin-motive force and spin-torque in Rashba SOC systems: The introduction of a strong Rashba spin orbit coupling (SOC) had been\npredicted to enhance the spin motive force (SMF) [see Phys. Rev. Lett. {\\bf\n108}, 217202 (2012)]. In this work, we predict further enhancement of the SMF\nby time modulation of the Rashba coupling $\\alpha_R$, which induces an\nadditional electric field $E^R_d={\\dot \\alpha_R} m_e/e\\hbar({\\hat z}\\times\n{\\mathbf m})$. When the modulation frequency is higher than the magnetization\nprecessing frequency, the amplitude of this field is significantly larger than\npreviously predicted results. Correspondingly, the spin torque on the\nmagnetization is also effectively enhanced. Additionally, the nature of SOC\ninduced spin torque in the system can be transformed from damping to\nantidamping-like by modulating ${\\dot \\alpha_R}$. We also suggest a biasing\nscheme to achieve rectification of SMF, {\\it i.e.}, by application of a square\nwave voltage at the resonant frequency. Finally, we numerically estimate the\nresulting spin torque field arising from a Gaussian pulse time modulation of\n$\\alpha_R$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spiral orientational order in quantum Hall skyrmion lattices: We investigate the existence of spiral ordering in the planar spin\norientation of skyrmions localised on a face centered rectangular lattice\n(FCRL). We use the non-linear sigma model (NLSM) to numerically calculate the\nminimum energy configurations of this lattice around the $\\nu=1$ quantum Hall\nground state. Our variational ansatz contains an angle $\\theta$, characterising\nthe FCRL and an angle $q$, characterising the orientational order. As $\\nu$ is\nincreased towards one, there is a smooth transition from the triangular lattice\n(TL) characterised by $(\\theta,q) = (120^o,120^o)$ to FCRLs with spiral\norientational order. The novel feature we find is that these phases are\ncharacterised by $\\theta, q)$ values such that $\\theta+q = 240^o$ (same as the\nTL phase). As $\\nu$ incresaes further towards one, there is a sharp transition\nfrom the FCRLs to the square lattice (SL), characterised by\n$(\\theta,q)=(90^o,180^o)$. Consequently, the parameter $\\theta+q$ jumps sharply\nat the FCRL-SL transition and can serve as an order parameter to characterise\nit.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Low frequency Raman studies of multi-wall carbon nanotubes: experiments\n  and theory: In this paper, we investigate the low frequency Raman spectra of multi-wall\ncarbon nanotubes (MWNT) prepared by the electric arc method. Low frequency\nRaman modes are unambiguously identified on purified samples thanks to the\nsmall internal diameter of the MWNT. We propose a model to describe these\nmodes. They originate from the radial breathing vibrations of the individual\nwalls coupled through the Van der Waals interaction between adjacent concentric\nwalls. The intensity of the modes is described in the framework of bond\npolarization theory. Using this model and the structural characteristics of the\nnanotubes obtained from transmission electron microscopy allows to simulate the\nexperimental low frequency Raman spectra with an excellent agreement. It\nsuggests that Raman spectroscopy can be as useful regarding the\ncharacterization of MWNT as it is in the case of single-wall nanotubes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical properties of the Hofstadter butterfly in the Moir\u00e9\n  superlattice: We investigate the optical absorption spectrum and the selection rule for the\nHofstadter butterfly in twisted bilayer graphene under magnetic fields. We\ndemonstrate that the absorption spectrum exhibits a self-similar recursive\npattern reflecting the fractal nature of the energy spectrum. We find that the\noptical selection rule has a nested self-similar structure as well, and it is\ngoverned by the conservation of the total angular momentum summed over\ndifferent hierarchies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Two components of donor-acceptor recombination in compensated\n  semiconductors. Analytical model of spectra in presence of electrostatic\n  fluctuations: We report numerical and analytical studies of the donor-acceptor\nrecombination in compensated semiconductors. Our calculations take into account\nrandom electric fields of charged impurities which are important in non zero\ncompensation case. We show that the donor-acceptor optical spectrum can be\ndescribed as a sum of two components: monomolecular and bimolecular. In the low\ncompensation limit we develop two analytical models for both types of the\nrecombination. Also our numerical simulation predicts that these two components\nof the photoluminescence spectra can be resolved under certain experimental\nconditions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Asymptotic Expressions for Charge Matrix Elements of the Fluxonium\n  Circuit: In charge-coupled circuit QED systems, transition amplitudes and dispersive\nshifts are governed by the matrix elements of the charge operator. For the\nfluxonium circuit, these matrix elements are not limited to nearest-neighbor\nenergy levels and are conveniently tunable by magnetic flux. Previously, their\nvalues were largely obtained numerically. Here, we present analytical\nexpressions for the fluxonium charge matrix elements. We show that new\nselection rules emerge in the asymptotic limit of large Josephson energy and\nsmall inductive energy. We illustrate the usefulness of our expressions for the\nqualitative understanding of charge matrix elements in the parameter regime\nprobed by previous experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Scanning Tunneling Microscopy and Spectroscopy of Graphene on Insulating\n  Substrates: Graphene is a truly two-dimensional material with exceptional electronic,\nmechanical, and optical properties. As such, it consists of surface only and\ncan be probed by the well developed surface-science techniques as, e.g.,\nscanning tunneling microscopy. This method bridges the gap between the surface\nscience community and the electronic device community and might lead to novel\ncombined approaches. Here, I review some of the scanning tunneling microscopy\n(STM) and spectroscopy (STS) experiments on monolayer graphene samples. I will\nconcentrate on graphene samples deposited on insulating substrates, since these\nare related to graphene device concepts. In particular, I will discuss the\nmorphology of graphene on SiO$_2$ and other emerging substrates, some\nnanomechanical manipulation experiments using STM, and spectroscopic results.\nThe latter can map the disorder potentials as well as the interaction of the\nelectrons with the disorder which is most pronounced in the quantum Hall\nregime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Rectification in mesoscopic AC-gated semiconductor devices: We measure the rectified dc currents resulting when a 3-terminal\nsemiconductor device with gate-dependent conductance is driven with an ac gate\nvoltage. The rectified currents exhibit surprisingly complex behaviour as the\ndc source-drain bias voltage, the dc gate voltage and the amplitude of the ac\ngate voltage are varied. We obtain good agreement between our data and a model\nbased on simple assumptions about the stray impedances on the sample chip, over\na wide frequency range. This method is applicable to many types of experiment\nwhich involve ac gating of a non-linear device, and where an undesireable\nrectified contribution to the measured signal is present. Finally, we evaluate\nthe small rectified currents flowing in tunable-barrier electron pumps operated\nin the pinched-off regime. These currents are at most $10^{-12}$ of the pumped\ncurrent for a pump current of 100 pA. This result is encouraging for the\ndevelopment of tunable-barrier pumps as metrological current standards.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nonequilibrium edge transport in quantum Hall based Josephson junctions: We study the transport properties of a voltage-biased Josephson junction\nwhere the BCS superconducting leads are coupled via the edges of a quantum Hall\nsample. In this scenario, an out of equilibrium Josephson current develops,\nwhich is numerically studied within the Floquet-Keldysh Green's function\nformalism. We particularly focus on the time-averaged current as a function of\nboth the bias voltage and the magnetic flux threading the sample and analyze\nthe resonant multiple Andreev reflection processes that lead to an enhancement\nof the quasiparticle transmission. We find that a full tomography of the dc\ncurrent in the voltage-flux plane allows for a complete spectroscopy of the\none-way edge modes and could be used as a hallmark of chiral edge mediated\ntransport in these hybrid devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Josephson Current in Ballistic Graphene Corbino Disk: We solve Dirac-Bogoliubov-De-Gennes (DBdG) equation in a\nsuperconductor-normal graphene superconductor (SGS) junction with Corbino disk\nstructure to investigate the Josephson current through this junction. We find\nthat the critical current $I_c$ has a nonzero value at Dirac point in which the\nconcentration of the carriers is zero. We show this nonzero critical current\ndepends on the system geometry and it decreases monotonically to zero by\nincreasing the ratio of the outer to inner radii of the Corbino disk\n($R_2/R_1$), while in the limit of $R_2/R_1 \\rightarrow 1$ it scales like a\ndiffusive Corbino disk. The product of the critical current and the\nnormal-state resistance $I_cR_N$ attains the same value for the planar\nstructure at zero doping. These results reveals the pseudodiffusive behavior of\nthe graphene Corbino Josephson junction similar to the planar structure.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Charge to Magnetic Flux Ratios: It is shown that if the carriers in the fractional quantum Hall effect are\ntaken as geometrical excitations with quanta of charge e and magnetic flux\nh/2e, as proposed in a previous publication, the calculated results are\ncompatible with the series of fractions obtained experimentally.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Homogenization of Rough Surfaces: Effective Surface Stress and\n  Superficial Elasticity: Relating microstructure to properties, electromagnetic, mechanical, thermal\nand their couplings has been a major focus of mechanics, physics and materials\nscience. The majority of the literature focuses on deriving homogenized\nconstitutive responses for macroscopic composites relating effective properties\nto various microstructural details. Due to large surface to volume ratio,\nphenomena at the nanoscale require consideration of surface energy effects and\nthe latter are frequently used to interpret size-effects in material behavior.\nElucidation of the effect of surface roughness on the surface stress and\nelastic behavior is relatively under-studied and quite relevant to the behavior\nof nanostructures. In this work, we present derivations that relate both\nperiodic and random roughness to the effective surface elastic behavior. We\nfind that the residual surface stress is hardly affected by roughness while the\nsuperficial elasticity properties are dramatically altered and, importantly,\nmay also result in a change in its sign - this has ramifications in\ninterpretation of sensing based on frequency measurement changes due to surface\nelasticity. We show that the square of resonance frequency of a cantilever beam\nwith rough surface decreases as much as three times of its value for flat\nsurface.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic catalysis and axionic charge-density-wave in Weyl semimetals: Three-dimensional Weyl and Dirac semimetals can support a\nchiral-symmetry-breaking, fully gapped, charge-density-wave order even for\nsufficiently weak repulsive electron-electron interactions, when placed in\nstrong magnetic fields. In the former systems, due to the natural momentum\nspace separation of Weyl nodes the ordered phase lacks the translational\nsymmetry and represents an axionic phase of matter, while that in a Dirac\nsemimetal (neglecting the Zeeman coupling) is only a trivial insulator. We\npresent the scaling of this spectral gap for a wide range of subcritical (weak)\ninteractions as well as that of the diamagnetic susceptibility with the\nmagnetic field. A similar mechanism for charge-density-wave ordering at weak\ncoupling is shown to be operative in double and triple-Weyl semimetals, where\nthe dispersion is linear (quadratic and cubic, respectively) for the z (planar)\ncomponent(s) of the momentum. We here also address the competition between the\ncharge-density-wave and a spin-density-wave orders, both of which breaks the\nchiral symmetry and leads to gapped spectrum, and show that at least in the\nweak coupling regime the former is energetically favored. The anomalous surface\nHall conductivity, role of topological defects such as axion strings, existence\nof one-dimensional gapless dispersive modes along the core of such defects, and\nanomaly cancellation through the Callan-Harvey mechanism are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nearly flat bands in twisted triple bilayer graphene: We investigate the electronic structure of alternating-twist triple\nBernal-stacked bilayer graphene (t3BG) as a function of interlayer coupling\n$\\omega$, twist angle $\\theta$, interlayer potential difference $\\Delta$, and\ntop-bottom bilayers sliding vector $\\boldsymbol{\\tau}$ for three possible\nconfigurations AB/AB/AB, AB/BA/AB, and AB/AB/BA. The parabolic low-energy band\ndispersions in a Bernal-stacked bilayer and gap-opening through a finite\ninterlayer potential difference $\\Delta$ allows the flattening of bands in t3BG\ndown to $\\sim 20$~meV for twist angles $\\theta \\lesssim 2^{\\circ}$ regardless\nof the stacking types. The easier isolation of the flat bands and associated\nreduction of Coulomb screening thanks to the intrinsic gaps of bilayer graphene\nfor finite $\\Delta$ facilitate the formation of correlation-driven gaps when it\nis compared to the metallic phases of twisted trilayer graphene under electric\nfields. We obtain the stacking dependent Coulomb energy versus bandwidth $U/W\n\\gtrsim 1$ ratios in the $\\theta$ and $\\Delta$ parameter space. We also present\nthe expected $K$-valley Chern numbers for the lowest-energy nearly flat bands.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current induced and interaction driven Dirac-point drag of massless\n  quasi-relativistic fermions: We study the quasiparticle properties of two-dimensional massless Dirac\nFermions when the many-body states possess a finite momentum density in the\nclean limit. The lack of Galilean invariance endows the many-body states at\nfinite momentum density with qualitative differences from those of the system\nat rest. At finite carrier densities we demonstrate the appearance of a\ncurrent-induced distortion of the pseudospin texture in momentum space that can\nbe viewed as a drag of the Dirac point and the origin of which lies entirely in\nelectron-electron interactions. We discuss the potential observation of this\neffect in graphene.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Acoustic phonon dynamics in thin-films of the topological insulator\n  Bi2Se3: Transient reflectivity traces measured for nanometer-sized films of the\ntopological insulator Bi2Se3 revealed GHz-range oscillations driven within the\nrelaxation of hot carriers photoexcited with ultrashort laser pulses of 1.51 eV\nphoton energy. These oscillations have been suggested to result from acoustic\nphonon dynamics, including coherent longitudinal acoustic phonons in the form\nof standing acoustic waves. An increase of oscillation frequency from ~35 to\n~70 GHz with decreasing film thickness from 40 to 15 nm was attributed to the\ninterplay between two different regimes employing traveling-acoustic-waves for\nfilms thicker than 40 nm and the film bulk acoustic wave resonator (FBAWR)\nmodes for films thinner than 40 nm. The amplitude of oscillations decays\nrapidly for films below 15 nm thick when the indirect intersurface coupling in\nBi2Se3 films switches the FBAWR regime to that of the Lamb wave excitation. The\nfrequency range of coherent longitudinal acoustic phonons is in good agreement\nwith elastic properties of Bi2Se3.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strain impacts on commensurate bilayer graphene superlattices: distorted\n  trigonal warping, emergence of bandgap and direct-indirect bandgap transition: Due to low dimensionality, the controlled stacking of the graphene films and\ntheir electronic properties are susceptible to environmental changes including\nstrain. The strain-induced modification of the electronic properties such as\nthe emergence and modulation of bandgaps crucially depends on the stacking of\nthe graphene films. However, to date, only the impact of strain on electronic\nproperties of Bernal and AA-stacked bilayer graphene has been extensively\ninvestigated in theoretical studies. Exploiting density functional theory and\ntight-binding calculation, we investigate the impacts of in-plane strain on two\ndifferent class of commensurate twisted bilayer graphene (TBG) which are\neven/odd under sublattice exchange (SE) parity. We find that the SE odd TBG\nremains gapless whereas the bandgap increases for the SE even TBG when applying\nequibiaxial tensile strain. Moreover, we observe that for extremely large mixed\nstrains both investigated TBG superstructures demonstrate direct-indirect\nbandgap transition.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electromagnetic properties of a double layer graphene system with\n  electron-hole pairing: We study electromagnetic properties of a double layer graphene system in\nwhich electrons from one layer are coupled with holes from the other layer. The\ngauge invariant linear response functions are obtained. The frequency\ndependences of the transmission, reflection and absorption coefficients are\ncomputed. We predict a peak in the reflection and absorption at the frequency\nequals to the gap in the quasiparticle spectrum. It is shown that the\nelectron-hole pairing results in an essential modification of the spectrum of\nsurface TM plasmons. We find that the optical TM mode splits into a low\nfrequency undamped branch and a high frequency damped branch. At zero\ntemperature the lower branch disappears. It is established that the pairing\ndoes not influence the acoustic TM mode. It is also shown that the pairing\nopens the frequency window in the subgap range for the surface TE wave.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Direct surface charging and alkali-metal doping for tuning the\n  interlayer magnetic order in planar nanostructures: The continuous reduction of magnetic units to ultra small length scales\ninspires efforts to look for a suitable means of controlling magnetic states.\nIn this study we show two surface charge alteration techniques for tuning the\ninterlayer exchange coupling (IEC) of ferromagnetic layers separated by\nparamagnetic spacers. Our study reveals that already a modest amount of extra\ncharge can switch the mutual alignment of the magnetization from\nanti-ferromagnetic to ferromagnetic or vice verse. We also propose adsorption\nof alkali metals as an alternative way of varying the electronic and chemical\nproperties of magnetic surfaces. Clear evidence is found that the interlayer\nmagnetic order can be reversed by adsorbing alkali metals on the magnetic\nlayer. Moreover, alkali metal overlayers strongly enhance the perpendicular\nmagnetic anisotropy in FePt thin films. These findings combined with atomistic\nspin model calculations suggest that electronic or ionic way of surface\ncharging can have a crucial role for magnetic hardening and spin state control.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fast preparation of single hole spin in InAs/GaAs quantum dot in Voigt\n  geometry magnetic field: The preparation of a coherent heavy-hole spin via ionization of a\nspin-polarized electron-hole pair in an InAs/GaAs quantum dot in a Voigt\ngeometry magnetic field is investigated. For a dot with a 17 ueV bright-exciton\nfine-structure splitting, the fidelity of the spin preparation is limited to\n0.75, with optimum preparation occurring when the effective fine-structure of\nthe bright-exciton matches the in-plane hole Zeeman energy. In principle,\nhigher fidelities can be achieved by minimizing the bright-exciton\nfine-structure splitting.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Evaluation of Spin Waves and Ferromagnetic Resonance Contribution to the\n  Spin Pumping in Ta/CoFeB Structure: The spin waves and ferromagnetic resonance (FMR) contribution to the spin\npumping signal is studied in the Ta/CoFeB interface under different excitation\nbias fields. Ferromagnetic resonance is excited utilizing a coplanar waveguide\nand a microwave generator. Using a narrow waveguide of about 3 {\\mu}m,\nmagnetostatic surface spin waves with large wavevector (k) of about 0.81\n{\\mu}m^-1 are excited. A large k value results in dissociation of spin waves\nand FMR frequencies according to the surface spin wave dispersion relation.\nSpin waves and FMR contribution to the spin pumping are calculated based on the\narea under the Lorentzian curve fitting over experimental results. It is found\nthat the FMR over spin waves contribution is about 1 at large bias fields in\nTa/CoFeB structure. Based on our spin pumping results, we propose a method to\ncharacterize the spin wave decay constant which is found to be about 5.5 {\\mu}m\nin the Ta/CoFeB structure at a bias field of 600 Oe.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Continuous microwave hole burning and population oscillations in a\n  diamond spin ensemble: Continuous spectral hole burning and spin-level population oscillations are\nstudied in an inhomogeneously broadened diamond-based spin ensemble composed of\nsubstitutional nitrogen and nitrogen-vacancy centres created through neutron\nirradiation and annealing. The burnt spectral features highlight a\ndetuning-dependent homogeneous hole linewidth that is up to three orders of\nmagnitude narrower than the total inhomogeneous ensemble linewidth. Continuous\npopulation oscillations are observed to quickly decay beyond a pump and probe\ndetuning of 5 Hz, and are numerically modelled using a five-level system of\ncoupled rate equations. Fourier analysis of these oscillations highlight\ndiscrete $^{13}$C hyperfine interactions, with energies within the\ninhomogeneous ensemble linewidth, as well as suspected nuclear $3/2$-spin\ncoupled signatures likely related to the $^7$Li byproduct of neutron\nirradiation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interface traps in graphene field effect devices: extraction methods and\n  influence on characteristics: We study impact of the near-interfacial oxide traps on the C-V and I-V\ncharacteristics of graphene gated structures. Methods of extraction of\ninterface trap level density in graphene field effect devices from the\ncapacitance-voltage measurements are described and discussed. It has been found\nthat the effects of electron-electron or hole-hole interactions and\nelectron-hole puddles can be mixed in C-V characteristics putting obstacles in\nthe way of uniquely determined extraction of the interface trap density in\ngraphene. Influence of the interface traps on DC and AC capacitance and\nconductance characteristics of graphene field-effect structures is described.\nIt has been shown that variety of widths of resistivity peaks in various\nsamples could be explained by different interface trap capacitance values.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Pseudospin, velocity and Berry phase in a bilayer graphene: Hamiltonian and eigenstate problem is formulated for a bilayer graphene in\nterms of Clifford's geometric algebra \\textit{Cl}$_{3,1}$. It is shown that\nsuch approach allows to perform analytical calculations in a simple way if\ngeometrical algebra rotors are used. The measured quantities are express\nthrough spectrum and rotation half-angle of the pseudospin that appears in\ngeometric algebra rotors. Properties of free charge carriers -- pseudospin,\nvelocity and Berry phase -- in a bilayer graphene are investigated in the\npresence of the external voltage applied between the two layers.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Chiral magnetic effect at finite temperature in a field-theoretic\n  approach: We investigate the existence (or lack thereof) of the chiral magnetic effect\nin the framework of finite temperature field theory, studied through the path\nintegral approach and regularized via the zeta function technique. We show\nthat, independently of the temperature, gauge invariance implies the absence of\nthe effect, a fact proved, at zero temperature and in a Hamiltonian approach,\nby N. Yamamoto. Indeed, the effect only appears when the manifold is finite in\nthe direction of the magnetic field and gauge-invariance breaking boundary\nconditions are imposed. We present an explicit calculation for antiperiodic and\nperiodic boundary conditions, which do allow for a CME, since only large gauge\ntransformations are, then, an invariance of the theory. In both cases, the\nassociated current does depend on the temperature, a well as on the size of the\nsample in the direction of the magnetic field, even for a\ntemperature-independent chiral chemical potential. In particular, for\nantiperiodic boundary conditions, the value of this current only agrees with\nthe result usually quoted in the literature on the subject in the\nzero-temperature limit, while it decreases with the temperature in a\nwell-determined way.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Relation between spin Hall effect and anomalous Hall effect in 3$d$\n  ferromagnetic metals: We study the mechanisms of the spin Hall effect (SHE) and anomalous Hall\neffect (AHE) in 3$d$ ferromagnetic metals (Fe, Co, permalloy\n(Ni$_{81}$Fe$_{19}$; Py), and Ni) by varying their resistivities and\ntemperature. At low temperatures where the phonon scattering is negligible, the\nskew scattering coefficients of the SHE and AHE in Py are related to its spin\npolarization. However, this simple relation breaks down for Py at higher\ntemperatures as well as for the other ferromagnetic metals at any temperature.\nWe find that, in general, the relation between the SHE and AHE is more complex,\nwith the temperature dependence of the SHE being much stronger than that of\nAHE.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Minimal models for nonreciprocal amplification using biharmonic drives: We present a generic system of three harmonic modes coupled parametrically\nwith a time-varying coupling modulated by a combination of two pump harmonics,\nand show how this system provides the minimal platform to realize nonreciprocal\ncouplings that can lead to gainless photon circulation, and phase-preserving or\nphase-sensitive directional amplification. Explicit frequency-dependent\ncalculations within this minimal paradigm highlight the separation of\namplification and directionality bandwidths, universal in such schemes. We also\nstudy the influence of counter-rotating interactions that can adversely affect\ndirectionality and associated bandwidth; we find that these effects can be\nmitigated by suitably designing the properties of the auxiliary mode that plays\nthe role of an engineered reservoir to the amplification mode space.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Microwave-induced magnetoresistance of two-dimensional electrons\n  interacting with acoustic phonons: The influence of electron-phonon interaction on magnetotransport in\ntwo-dimensional electron systems under microwave irradiation is studied\ntheoretically. Apart from the phonon-induced resistance oscillations which\nexist in the absence of microwaves, the magnetoresistance of irradiated samples\ncontains oscillating contributions due to electron scattering on both\nimpurities and acoustic phonons. The contributions due to electron-phonon\nscattering are described as a result of the interference of phonon-induced and\nmicrowave-induced resistance oscillations. In addition, microwave heating of\nelectrons leads to a special kind of phonon-induced oscillations. The relative\nstrength of different contributions and their dependence on parameters are\ndiscussed. The interplay of numerous oscillating contributions suggests a\npeculiar magnetoresistance picture in high-mobility layers at the temperatures\nwhen electron-phonon scattering becomes important.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport properties and electrical device characteristics with the\n  TiMeS computational platform: application in silicon nanowires: Nanoelectronics requires the development of a priori technology evaluation\nfor materials and device design that takes into account quantum physical\neffects and the explicit chemical nature at the atomic scale. Here, we present\na cross-platform quantum transport computation tool. Using first-principles\nelectronic structure, it allows for flexible and efficient calculations of\nmaterials transport properties and realistic device simulations to extract\ncurrent-voltage and transfer characteristics. We apply this computational\nmethod to the calculation of the mean free path in silicon nanowires with\ndopant and surface oxygen impurities. The dependence of transport on basis set\nis established, with the optimized double zeta polarized basis giving a\nreasonable compromise between converged results and efficiency. The\ncurrent-voltage characteristics of ultrascaled (3 nm length) nanowire-based\ntransistors with p-i-p and p-n-p doping profiles are also investigated. It is\nfound that charge self-consistency affects the device characteristics more\nsignificantly than the choice of the basis set. These devices yield\nsource-drain tunneling currents in the range of 0.5 nA (p-n-p junction) to 2 nA\n(p-i-p junction), implying that junctioned transistor designs at these length\nscales would likely fail to keep carriers out of the channel in the off-state.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Symmetry dictated universal helicity redistribution of Dirac fermions in\n  transport: Helicity is a fundamental property of Dirac fermions. Yet, the general rule\nof how it changes in transport is still lacking. We uncover, theoretically, the\nuniversal spinor state transformation and consequently helicity redistribution\nrule in two cases of transport through potentials of electrostatic and mass\ntypes, respectively. The former is dictated by Lorentz boost and its complex\ncounterpart in Klein tunneling regime, which establishes miraculously a unified\nyet latent connection between helicity, Klein tunneling, and Lorentz boost. The\nlatter is governed by an abstract rotation group we construct, which reduces to\nSO(2) when acting on the plane of effective mass and momentum. They generate\ninvariant submanifolds, i.e., leaves, that foliate the Hilbert space of Dirac\nspinors. Our results provide a basis for unified understanding of helicity\ntransport, and may open a new window for exotic helicity-based physics and\napplications in mesoscopic systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Composite Fermions with a Warped Fermi Contour: Via measurements of commensurability features near Landau filling factor\n$\\nu=1/2$, we probe the shape of the Fermi contour for hole-flux composite\nfermions confined to a wide GaAs quantum well. The data reveal that the\ncomposite fermions are strongly influenced by the characteristics of the Landau\nlevel in which they are formed. In particular, their Fermi contour is\n$\\textit{warped}$ when their Landau level originates from a hole band with\nsignificant warping.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Signatures of folded branches in the scanning gate microscopy of\n  ballistic electronic cavities: We demonstrate the emergence of classical features in electronic quantum\ntransport for the scanning gate microscopy response in a cavity defined by a\nquantum point contact and a micron-sized circular reflector. The branches in\nelectronic flow characteristic of a quantum point contact opening on a\ntwo-dimensional electron gas with weak disorder are folded by the reflector,\nyielding a complex spatial pattern. Considering the deflection of classical\ntrajectories by the scanning gate tip allows to establish simple relationships\nof the scanning pattern, which are in agreement with recent experimental\nfindings.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spectroscopy of double quantum dot two-spin states by tuning the\n  inter-dot barrier: Transport spectroscopy of two-spin states in a double quantum dot can be\nperformed by an AC electric field which tunes the energy detuning. However, a\nproblem arises when the transition rate between the states is small and,\nconsequently, the AC-induced current is suppressed. Here, we show that if the\nAC field tunes the inter-dot tunnel barrier then for large detuning the\ntransition rate increases drastically resulting in high current. Multi-photon\nresonances are enhanced by orders of magnitude. Our study demonstrates an\nefficient way for fast two-spin transitions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Proximity DC squids in the long junction limit: We report the design and measurement of\nSuperconducting/normal/superconducting (SNS) proximity DC squids in the long\njunction limit, i.e. superconducting loops interrupted by two normal metal\nwires roughly a micrometer long. Thanks to the clean interface between the\nmetals, at low temperature a large supercurrent flows through the device. The\ndc squid-like geometry leads to an almost complete periodic modulation of the\ncritical current through the device by a magnetic flux, with a flux periodicity\nof a flux quantum h/2e through the SNS loop. In addition, we examine the entire\nfield dependence, notably the low and high field dependence of the maximum\nswitching current. In contrast with the well-known Fraunhoffer-type\noscillations typical of short wide junctions, we find a monotonous gaussian\nextinction of the critical current at high field. As shown in [15], this\nmonotonous dependence is typical of long and narrow diffusive junctions. We\nalso find in some cases a puzzling reentrance at low field. In contrast, the\ntemperature dependence of the critical current is well described by the\nproximity effect theory, as found by Dubos {\\it et al.} [16] on SNS wires in\nthe long junction limit. The switching current distributions and hysteretic IV\ncurves also suggest interesting dynamics of long SNS junctions with an\nimportant role played by the diffusion time across the junction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interaction effects on thermal transport in quantum wires: We develop a theory of thermal transport of weakly interacting electrons in\nquantum wires. Unlike higher-dimensional systems, a one-dimensional electron\ngas requires three-particle collisions for energy relaxation. The fastest\nrelaxation is provided by the intrabranch scattering of comoving electrons\nwhich establishes a partially equilibrated form of the distribution function.\nThe thermal conductance is governed by the slower interbranch processes which\nenable energy exchange between counterpropagating particles. We derive an\nanalytic expression for the thermal conductance of interacting electrons valid\nfor arbitrary relation between the wire length and electron thermalization\nlength. We find that in sufficiently long wires the interaction-induced\ncorrection to the thermal conductance saturates to an interaction-independent\nvalue.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin Coulomb drag by non-equilibrium magnetic textures: Interaction between local magnetization and conduction electrons is\nresponsible for a variety of phenomena in magnetic materials. We have shown\nthat the spin-dependent motive force induced by magnetization dynamics in a\nconducting ferromagnet lead to the spin Coulomb drag effect. The spin Coulomb\ndrag an intrinsic friction mechanism which operates whenever the average\nvelocities of up-spin and down-spin electrons differ.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Single ion implantation for single donor devices using Geiger mode\n  detectors: Electronic devices that are designed to use the properties of single atoms\nsuch as donors or defects have become a reality with recent demonstrations of\ndonor spectroscopy, single photon emission sources, and magnetic imaging using\ndefect centers in diamond. Improving single ion detector sensitivity is linked\nto improving control over the straggle of the ion as well as providing more\nflexibility in lay-out integration with the active region of the single donor\ndevice construction zone by allowing ion sensing at potentially greater\ndistances. Using a remotely located passively gated single ion Geiger mode\navalanche diode (SIGMA) detector we have demonstrated 100% detection efficiency\nat a distance of >75 um from the center of the collecting junction. This\ndetection efficiency is achieved with sensitivity to ~600 or fewer\nelectron-hole pairs produced by the implanted ion. Ion detectors with this\nsensitivity and integrated with a thin dielectric, for example 5 nm gate oxide,\nusing low energy Sb implantation would have an end of range straggle of <2.5\nnm. Significant reduction in false count probability is achieved by modifying\nthe ion beam set-up to allow for cryogenic operation of the SIGMA detector.\nUsing a detection window of 230 ns at 1 Hz, the probability of a false count\nwas measured as 1E-1 and 1E-4 for operation temperatures of 300K and 77K,\nrespectively. Low temperature operation and reduced false, dark, counts are\ncritical to achieving high confidence in single ion arrival. For the device\nperformance in this work, the confidence is calculated as a probability of >98%\nfor counting one and only one ion for a false count probability of 1E-4 at an\naverage ion number per gated window of 0.015.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamical Lamb Effect in a Tunable Superconducting Qubit-Cavity System: A natural atom placed into a cavity with time-dependent parameters can be\nparametrically excited due to the interaction with the quantized photon mode.\nOne of the channels of such a process is the dynamical Lamb effect, induced by\na nonadiabatic modulation of atomic level Lamb shift. However, in experiments\nwith natural atoms it is quite difficult to isolate this effect from other\nmechanisms of atom excitation. We point out that a transmission line cavity\ncoupled with a superconducting qubit (artificial macroscopic atom) provides a\nunique platform for the observation of the dynamical Lamb effect. A key idea is\nto exploit a dynamically tunable qubit-resonator coupling, which was\nimplemented quite recently. By varying nonadiabatically the coupling, it is\npossible to parametrically excite a qubit through a nonadiabatic modulation of\nthe Lamb shift, even if the cavity was initially empty. A dynamics of such a\ncoupled system is studied within the Rabi model with time-dependent coupling\nconstant and beyond the rotating wave approximation. An efficient method to\nincrease the effect through the periodic and nonadiabatic switching of a\nqubit-resonator coupling energy is proposed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "All-optical hyperpolarization of electron and nuclear spins in diamond: Low thermal polarization of nuclear spins is a primary sensitivity limitation\nfor nuclear magnetic resonance. Here we demonstrate optically pumped\n(microwave-free) nuclear spin polarization of $^{13}\\mathrm{C}$ and\n$^{15}\\mathrm{N}$ in $^{15}\\mathrm{N}$-doped diamond. $^{15}\\mathrm{N}$\npolarization enhancements up to $-2000$ above thermal equilibrium are observed\nin the paramagnetic system $\\mathrm{N_s}^{0}$. Nuclear spin polarization is\nshown to diffuse to bulk $^{13}\\mathrm{C}$ with NMR enhancements of $-200$ at\nroom temperature and $-500$ at $\\mathrm{240~K}$, enabling a route to\nmicrowave-free high-sensitivity NMR study of biological samples in ambient\nconditions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Many-body approach to non-Hermitian physics in fermionic systems: In previous studies, the topological invariants of 1D non-Hermitian systems\nhave been defined in open boundary condition (OBC) to satisfy the bulk-boundary\ncorrespondence. The extreme sensitivity of bulk energy spectra to boundary\nconditions has been attributed to the breakdown of the conventional\nbulk-boundary correspondence based on the topological invariants defined under\nperiodic boundary condition (PBC). Here we propose non-Hermitian many-body\npolarization as a topological invariant for 1D non-Hermitian systems defined in\nPBC, which satisfies the bulk-boundary correspondence. Employing many-body\nmethodology in the non-Hermitian Su-Schrieffer-Heeger model for fermions, we\nshow the absence of non-Hermitian skin effect due to the Pauli exclusion\nprinciple and demonstrate the bulk-boundary correspondence using the invariant\ndefined under PBC. Moreover, we show that the bulk topological invariant is\nquantized in the presence of chiral or generalized inversion symmetry. Our\nstudy suggests the existence of generalized crystalline symmetries in\nnon-Hermitian systems, which give quantized topological invariants that capture\nthe symmetry-protected topology of non-Hermitian systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Equilibrium current vortices in rare-earth-doped simple metals: Dilute alloys of rare earths have played a vital role in understanding\nmagnetic phenomena. Here, we model the ground state of dilute 4f rare-earth\nimpurities in light metals. When the 4f subshells are open (but not\nhalf-filled), the spin-orbit coupling imprints a rotational charge current of\nconduction electrons around rare-earth atoms. The sign and amplitude of the\ncurrent oscillate similar to the RKKY spin polarization. We compute the\nobservable effect, namely the Oersted field generated by the current vortices\nand the Knight shift.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current-controlled light scattering and asymmetric plasmon propagation\n  in graphene: We demonstrate that plasmons in graphene can be manipulated using a DC\ncurrent. A source-drain current lifts the forward/backward degeneracy of the\nplasmons, creating two modes with different propagation properties parallel and\nantiparallel to the current. We show that the propagation length of the plasmon\npropagating parallel to the drift current is enhanced, while the propagation\nlength for the antiparallel plasmon is suppressed. We also investigate the\nscattering of light off graphene due to the plasmons in a periodic dielectric\nenvironment and we find that the plasmon resonance separates in two peaks\ncorresponding to the forward and backward plasmon modes. The narrower linewidth\nof the forward propagating plasmon may be of interest for refractive index\nsensing and the DC current control could be used for the modulation of\nmid-infrared electromagnetic radiation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Particle-Flux Separation and Quasiexcitations in Quantum Hall Systems: The quasiexcitations of quantum Hall systems at the filling factor $\\nu =\np/(2pq \\pm 1)$ are studied in terms of chargeon and fluxon introduced\npreviously as constituents of an electron at $\\nu = 1/2$. At temperatures $T <\nT_{\\rm PFS}(\\nu)$, the phenomenon so-called particle-flux separation takes\nplace, and chargeons and fluxons are deconfined to behave as quasiparticles.\nBose condensation of fluxons justify the (partial) cancellation of external\nmagnetic field. Fluxons describe correlation holes, while chargeons describe\ncomposite fermions. They contribute to the resistivity $\\rho_{xy} = h/(\\nu\ne^2)$ additively.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Percolation via combined electrostatic and chemical doping in complex\n  oxide films: Stimulated by experimental advances in electrolyte gating methods, we\ninvestigate theoretically percolation in thin films of inhomogenous complex\noxides, such as La$_{1-x}$Sr$_{x}$CoO$_{3}$ (LSCO), induced by a combination of\nbulk chemical and surface electrostatic doping. Using numerical and analytical\nmethods, we identify two mechanisms that describe how bulk dopants reduce the\namount of electrostatic surface charge required to reach percolation: (i)\nbulk-assisted surface percolation, and (ii) surface-assisted bulk percolation.\nWe show that the critical surface charge strongly depends on the film thickness\nwhen the film is close to the chemical percolation threshold. In particular,\nthin films can be driven across the percolation transition by modest surface\ncharge densities \\emph{via} surface-assisted bulk percolation. If percolation\nis associated with the onset of ferromagnetism, as in LSCO, we further\ndemonstrate that the presence of critical magnetic clusters extending from the\nfilm surface into the bulk results in considerable volume enhancement of the\nsaturation magnetization, with pronounced experimental consequences. These\nresults should significantly guide experimental work seeking to verify\ngate-induced percolation transitions in such materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum criticality in a double quantum-dot system: We discuss the realization of the quantum-critical non-Fermi liquid state,\noriginally discovered within the two-impurity Kondo model, in double\nquantum-dot systems. Contrary to the common belief, the corresponding fixed\npoint is robust against particle-hole and various other asymmetries, and is\nonly unstable to charge transfer between the two dots. We propose an\nexperimental set-up where such charge transfer processes are suppressed,\nallowing a controlled approach to the quantum critical state. We also discuss\ntransport and scaling properties in the vicinity of the critical point.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Scaling analysis of Kondo screening cloud in a mesoscopic ring with an\n  embedded quantum dot: The Kondo effect is theoretically studied in a quantum dot embedded in a\nmesoscopic ring. The ring is connected to two external leads, which enables the\ntransport measurement. Using the \"poor man's\" scaling method, we obtain\nanalytical expressions of the Kondo temperature T_K as a function of the\nAharonov-Bohm phase \\phi by the magnetic flux penetrating the ring. In this\nKondo problem, there are two characteristic lengths. One is the screening\nlength of the charge fluctuation, L_c=\\hbar v_F/ |\\epsilon_0|, where v_F is the\nFermi velocity and \\epsilon_0 is the energy level in the quantum dot. The other\nis the screening length of spin fluctuation, i.e., size of Kondo screening\ncloud, L_K=\\hbar v_F/ T_K. We obtain different expressions of T_K(\\phi) for (i)\nL_c \\ll L_K \\ll L, (ii) L_c \\ll L \\ll L_K, and (iii) L \\ll L_c \\ll L_K, where L\nis the size of the ring. T_K is markedly modulated by \\phi in cases (ii) and\n(iii), whereas it hardly depends on \\phi in case (i). We also derive\nlogarithmic corrections to the conductance at temperature T\\gg T_K and an\nanalytical expression of the conductance at T\\ll T_K, on the basis of the\nscaling analysis.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Collective modes in interacting two-dimensional tomographic Fermi\n  liquids: We develop an analytically solvable model for interacting two-dimensional\nFermi liquids with separate collisional relaxation rates for parity-odd and\nparity-even Fermi surface deformations. Such a disparity of collisional\nlifetimes exists whenever scattering is restricted to inversion-symmetric Fermi\nsurfaces, and should thus be a generic feature of two-dimensional Fermi\nliquids. It implies an additional unanticipated \"tomographic\" transport regime\n(in between the standard collisionless and hydrodynamic regimes) in which\neven-parity modes are overdamped while odd-parity modes are collisionless. We\nderive expressions for both the longitudinal and the transverse conductivity\nand discuss the collective mode spectrum along the\ncollisionless-tomographic-hydrodynamic crossover. Longitudinal modes cross over\nfrom zero sound in the collisionless regime to hydrodynamic first sound in the\ntomographic and hydrodynamic regime, where odd-parity damping appears as a\nsubleading correction to the lifetime. In charged Fermi liquids with long-range\nCoulomb coupling, these modes reduce to plasmons with a strongly suppressed\nodd-parity correction to the damping. The transverse response, by contrast, has\na specific tomographic transport regime with two imaginary odd-parity modes,\none of which requires a finite repulsive interaction, distinct from both the\nshear sound in the collisionless regime and an overdamped diffusive current\nmode in the hydrodynamic limit. Our work demonstrates that there are deep\nmany-body aspects of interacting Fermi liquids, which are often thought to be\nwell understood theoretically, remaining unexplored.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-orbit induced longitudinal spin-polarized currents in non-magnetic\n  solids: For certain non-magnetic solids with low symmetry the occurrence of\nspin-polarized longitudinal currents is predicted. These arise due to an\ninterplay of spin-orbit interaction and the particular crystal symmetry. This\nresult is derived using a group-theoretical scheme that allows investigating\nthe symmetry properties of any linear response tensor relevant to the field of\nspintronics. For the spin conductivity tensor it is shown that only the\nmagnetic Laue group has to be considered in this context. Within the introduced\ngeneral scheme also the spin Hall- and additional related transverse effects\nemerge without making reference to the two-current model. Numerical studies\nconfirm these findings and demonstrate for (Au$_{1-x}$Pt$_{\\rm x}$)$_4$Sc that\nthe longitudinal spin conductivity may be in the same order of magnitude as the\nconventional transverse one. The presented formalism only relies on the\nmagnetic space group and therefore is universally applicable to any type of\nmagnetic order.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Friedel oscillations induced by magnetic skyrmions: from scattering\n  properties to all-electrical detection: Magnetic skyrmions are spin swirling solitonic defects that can play a major\nrole in information technology. Their future in applications and devices hinges\non their efficient manipulation and detection. Here, we explore from ab-initio\ntheir nature as magnetic inhomongeities in an otherwise unperturbed magnetic\nmaterial, Fe layer covered by a thin Pd film and deposited on top of Ir(111)\nsurface. The presence of skyrmions triggers scattering processes, from which\nFriedel oscillations emerge. The latter mediate interactions among skyrmions or\nbetween skyrmions and other potential surrounding defects. In contrast to their\nwavelengths, the amplitude of the oscillations depends strongly on the size of\nthe skyrmion. The analogy with the scattering-off atomic defects enables the\nassignment of an effective scattering potential and a phase shift to the\nskyrmionic particles, which can be useful to predict their behavior on the\nbasis of simple scattering frameworks. The induced charge ripples can be\nutilized for a noninvasive all-electrical detection of skyrmions located on a\nsurface or even if buried a few nanometers away from the detecting electrode.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cotunneling renormalization in carbon nanotube quantum dots: We determine the level-shifts induced by cotunneling in a Coulomb blockaded\ncarbon nanotube quantum dot using leading order quasi-degenerate perturbation\ntheory within a single nanotube quartet. It is demonstrated that otherwise\ndegenerate and equally tunnel-coupled $K$ and $K'$ states are mixed by\ncotunneling and therefore split up in energy except at the\nparticle/hole-symmetric midpoints of the Coulomb diamonds. In the presence of\nan external magnetic field, we show that cotunneling induces a gate-dependent\n$g$-factor renormalization, and we outline different scenarios which might be\nobserved experimentally, depending on the values of both intrinsic $KK'$\nsplitting and spin-orbit coupling.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electrically controlling single spin qubits in a continuous microwave\n  field: Large-scale quantum computers must be built upon quantum bits that are both\nhighly coherent and locally controllable. We demonstrate the quantum control of\nthe electron and the nuclear spin of a single 31P atom in silicon, using a\ncontinuous microwave magnetic field together with nanoscale electrostatic\ngates. The qubits are tuned into resonance with the microwave field by a local\nchange in electric field, which induces a Stark shift of the qubit energies.\nThis method, known as A-gate control, preserves the excellent coherence times\nand gate fidelities of isolated spins, and can be extended to arbitrarily many\nqubits without requiring multiple microwave sources.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strong influence of spin-orbit coupling on magnetotransport in\n  two-dimensional hole systems: With a view to electrical spin manipulation and quantum computing\napplications, recent significant attention has been devoted to semiconductor\nhole systems, which have very strong spin-orbit interactions. However,\nexperimentally measuring, identifying, and quantifying spin-orbit coupling\neffects in transport, such as electrically-induced spin polarizations and\nspin-Hall currents, are challenging. Here we show that the magnetotransport\nproperties of two dimensional (2D) hole systems display strong signatures of\nthe spin-orbit interaction. Specifically, the low-magnetic field Hall\ncoefficient and longitudinal conductivity contain a contribution that is second\norder in the spin-orbit interaction coefficient and is non-linear in the\ncarrier number density. We propose an appropriate experimental setup to probe\nthese spin-orbit dependent magnetotransport properties, which will permit one\nto extract the spin-orbit coefficient directly from the magnetotransport.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Detection of finite frequency photo-assisted shot noise with a resonant\n  circuit: Photo-assisted transport through a mesoscopic conductor occurs when an\noscillatory (AC) voltage is superposed to the constant (DC) bias which is\nimposed on this conductor. Of particular interest is the photo assisted shot\nnoise, which has been investigated theoretically and experimentally for several\ntypes of samples. For DC biased conductors, a detection scheme for finite\nfrequency noise using a dissipative resonant circuit, which is inductively\ncoupled to the mesoscopic device, was developped recently. We argue that the\ndetection of the finite frequency photo-assisted shot noise can be achieved\nwith the same setup, despite the fact that time translational invariance is\nabsent here. We show that a measure of the photo-assisted shot noise can be\nobtained through the charge correlator associated with the resonant circuit,\nwhere the latter is averaged over the AC drive frequency. We test our\npredictions for a point contact placed in the fractional quantum Hall effect\nregime, for the case of weak backscattering. The Keldysh elements of the\nphoto-assisted noise correlator are computed. For simple Laughlin fractions,\nthe measured photo-assisted shot noise displays peaks at the frequency\ncorresponding to the DC bias voltage, as well as satellite peaks separated by\nthe AC drive frequency.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Composite Fermions in Negative Effective Magnetic Field: A Monte-Carlo\n  Study: The method of Jain and Kamilla [PRB {\\bf 55}, R4895 (1997)] allows numerical\ngeneration of composite fermion trial wavefunctions for large numbers of\nelectrons in high magnetic fields at filling fractions of the form nu=p/(2mp+1)\nwith m and p positive integers. In the current paper we generalize this method\nto the case where the composite fermions are in an effective (mean) field with\nopposite sign from the actual physical field, i.e. when p is negative. We\nexamine both the ground state energies and the low energy neutral excitation\nspectra of these states. Using particle-hole symmetry we can confirm the\ncorrectness of our method by comparing results for the series m=1 with p>0\n(previously calculated by others) to our results for the conjugate series m=1\nwith p <0. Finally, we present similar results for ground state energies and\nlow energy neutral excitations for the states with m=2 and p <0 which were not\npreviously addressable, comparing our results to the m=1 case and the p > 0,\nm=2 cases.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Charge trapping in the system of interacting quantum dots: We analyzed the localized charge dynamics in the system of $N$ interacting\nsingle-level quantum dots (QDs) coupled to the continuous spectrum states in\nthe presence of Coulomb interaction between electrons within the dots.\nDifferent dots geometry and initial charge configurations were considered. The\nanalysis was performed by means of Heisenberg equations for localized electrons\npair correlators.\n  We revealed that charge trapping takes place for a wide range of system\nparameters and we suggested the QDs geometry for experimental observations of\nthis phenomenon. We demonstrated significant suppression of Coulomb\ncorrelations with the increasing of QDs number. We found the appearance of\nseveral time scales with the strongly different relaxation rates for a wide\nrange of the Coulomb interaction values.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Low Temperature Nanoscale Electronic Transport on the MoS_2 surface: Two-probe electronic transport measurements on a Molybdenum Disulphide\n(MoS_2) surface were performed at low temperature (30K) under ultra-high vacuum\nconditions. Two scanning tunneling microscope tips were precisely positioned in\ntunneling contact to measure the surface current-voltage characteristics. The\nseparation between the tips is controllably varied and measured using a high\nresolution scanning electron microscope. The MoS_2 surface shows a surface\nelectronic gap (E_S) of 1.4eV measured at a probe separation of 50nm.\nFurthermore, the two- probe resistance measured outside the electronic gap\nshows 2D-like behavior with the two-probe separation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Crystalline Polymers with Exceptionally Low Thermal Conductivity Studied\n  using Molecular Dynamics: Semi-crystalline polymers have been shown to have greatly increased thermal\nconductivity compared to amorphous bulk polymers due to effective heat\nconduction along the covalent bonds of the backbone. However, the mechanisms\ngoverning the intrinsic thermal conductivity of polymers remain largely\nunexplored as thermal transport has been studied in relatively few polymers.\nHere, we use molecular dynamics simulations to study heat transport in\npolynorbornene, a polymer that can be synthesized in semi-crystalline form\nusing solution processing. We find that even perfectly crystalline\npolynorbornene has an exceptionally low thermal conductivity near the amorphous\nlimit due to extremely strong anharmonic scattering. Our calculations show that\nthis scattering is sufficiently strong to prevent the formation of propagating\nphonons, with heat being instead carried by non-propagating, delocalized\nvibrational modes known as diffusons. Our results demonstrate a mechanism for\nachieving intrinsically low thermal conductivity even in crystalline polymers\nthat may be useful for organic thermoelectrics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Structural and Electrical Characterization of Bi2Se3 Nanostructures\n  Grown by Metalorganic Chemical Vapor Deposition: We characterize nanostructures of Bi2Se3 that are grown via metalorganic\nchemical vapor deposition using the precursors diethyl selenium and trimethyl\nbismuth. By adjusting growth parameters, we obtain either single-crystalline\nribbons up to 10 microns long or thin micron-sized platelets. Four-terminal\nresistance measurements yield a sample resistivity of 4 mOhm-cm. We observe\nweak anti-localization and extract a phase coherence length l_phi = 178 nm and\nspin-orbit length l_so = 93 nm at T = 0.29 K. Our results are consistent with\nprevious measurements on exfoliated samples and samples grown via physical\nvapor deposition.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport Mean Free Path for Magneto-Transverse Light Diffusion: We derive an expression for the transport mean free path $\\ell^*_\\perp$\nassociated with magneto-transverse light diffusion for a random collection of\nFaraday-active\n  Mie scatterers. This expression relates the magneto-transverse diffusion in\nmultiple scattering directly to the magneto-transverse scattering of a single\nscatterer.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coherent Phonons in Carbon Nanotubes and Graphene: We review recent studies of coherent phonons (CPs) corresponding to the\nradial breathing mode (RBM) and G-mode in single-wall carbon nanotubes (SWCNTs)\nand graphene. Because of the bandgap-diameter relationship, RBM-CPs cause\nbandgap oscillations in SWCNTs, modulating interband transitions at terahertz\nfrequencies. Interband resonances enhance CP signals, allowing for chirality\ndetermination. Using pulse shaping, one can selectively excite\nspeci!c-chirality SWCNTs within an ensemble. G-mode CPs exhibit\ntemperature-dependent dephasing via interaction with RBM phonons. Our\nmicroscopic theory derives a driven oscillator equation with a\ndensity-dependent driving term, which correctly predicts CP trends within and\nbetween (2n+m) families. We also find that the diameter can initially increase\nor decrease. Finally, we theoretically study the radial breathing like mode in\ngraphene nanoribbons. For excitation near the absorption edge, the driving term\nis much larger for zigzag nanoribbons. We also explain how the armchair\nnanoribbon width changes in response to laser excitation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Stark effect and generalized Bloch-Siegert shift in a strongly driven\n  two-level system: A superconducting qubit was driven in an ultrastrong fashion by an\noscillatory microwave field, which was created by coupling via the nonlinear\nJosephson energy. The observed Stark shifts of the `atomic' levels are so\npronounced that corrections even beyond the lowest-order Bloch-Siegert shift\nare needed to properly explain the measurements. The quasienergies of the\ndressed two-level system were probed by resonant absorption via a cavity, and\nthe results are in agreement with a calculation based on the Floquet approach.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Near-field thermal transport between twisted bilayer graphene: Active control of heat flow is of both fundamental and applied interest in\nthermal management and energy conversion. Here, we present a fluctuational\nelectrodynamic study of thermal radiation between twisted bilayer graphene\n(TBLG), motivated by its unusual and highly tunable plasmonic properties. We\nshow that near-field heat flow can vary by more than 10-fold over only a few\ndegrees of twist, and identify special angles leading to heat flow extrema.\nThese special angles are dictated by the Drude weight in the intraband optical\nconductivity of TBLG, and are roughly linear with the chemical potential.\nFurther, we observe multiband thermal transport due to the increasing role of\ninterband transitions as the twist angle decreases, in analogy to monolayer\ngraphene in a magnetic field. Our findings are understood via the surface\nplasmons in TBLG, and highlight its potential for manipulating radiative heat\nflow.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Orbital Stark effect and quantum confinement transition of donors in\n  silicon: Adiabatic shuttling of single impurity bound electrons to gate induced\nsurface states in semiconductors has attracted much attention in recent times,\nmostly in the context of solid-state quantum computer architecture. A recent\ntransport spectroscopy experiment for the first time was able to probe the\nStark shifted spectrum of a single donor in silicon buried close to a gate.\nHere we present the full theoretical model involving large-scale quantum\nmechanical simulations that was used to compute the Stark shifted donor states\nin order to interpret the experimental data. Use of atomistic tight-binding\ntechnique on a domain of over a million atoms helped not only to incorporate\nthe full band structure of the host, but also to treat realistic device\ngeometries and donor models, and to use a large enough basis set to capture any\nnumber of donor states. The method yields a quantitative description of the\nsymmetry transition that the donor electron undergoes from a 3D Coulomb\nconfined state to a 2D surface state as the electric field is ramped up\nadiabatically. In the intermediate field regime, the electron resides in a\nsuperposition between the states of the atomic donor potential and that of the\nquantum dot like states at the surface. In addition to determining the effect\nof field and donor depth on the electronic structure, the model also provides a\nbasis to distinguish between a phosphorus and an arsenic donor based on their\nStark signature. The method also captures valley-orbit splitting in both the\ndonor well and the interface well, a quantity critical to silicon qubits. The\nwork concludes with a detailed analysis of the effects of screening on the\ndonor spectrum.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Phonons and Thermal Conducting Properties of Borocarbonitride (BCN)\n  Nanosheets: Hexagonal borocarbonitrides (BCN) are a class of 2D materials, which display\nexcellent catalytic activity for water splitting. Here, we report analysis of\nthermal stability, phonons and thermal conductivity of BCN monolayers over a\nwide range of temperatures using classical molecular dynamics simulations. Our\nresults show that in contrast to the case of graphene and boron nitride\nmonolayers, the out-of-plane phonons in BCN monolayers induce an asymmetry in\nthe phonon density of states at all temperatures. Despite possessing lower\nthermal conducting properties compared to graphene and BN monolayers, the BCN\nnanosheets do not lose thermal conductivity as much as graphene and BN in the\nstudied temperature range of 200-1000 K, and thus, the BCN nanosheets are\nsuitable for thermal interface device applications over a wide range of\ntemperatures. Besides their promising role in water splitting, the above\nresults highlight the possibility of expanding the use of BCN 2D materials in\nthermal management applications and thermoelectrics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Sensitivity of the Power Spectra of Magnetization Fluctuations in Low\n  Barrier Nanomagnets to Barrier Height Modulation and Defects: Nanomagnets with small shape anisotropy energy barriers on the order of the\nthermal energy have unstable magnetization that fluctuates randomly in time.\nThey have recently emerged as promising hardware platforms for stochastic\ncomputing and machine learning because the random magnetization states can be\nharnessed for probabilistic bits. Here, we have studied how the statistics of\nthe magnetization fluctuations (e.g. the power spectral density) is affected by\n(i) moderate variations in the barrier height of the nanomagnet and (ii) the\npresence of structural defects, in order to assess how robust the computing\nplatform is. We found that the power spectral density is relatively insensitive\nto moderate barrier height change and also relatively insensitive to the\npresence of small localized defects. However, extended (delocalized) defects,\nsuch as thickness variations over a significant fraction of the nanomagnet,\naffect the power spectral density very noticeably. As a result, small\nvariations in the shape (causing small variations in the barrier height), or\nsmall localized defects, are relatively innocuous and tolerable, but\nsignificant variation of the nanomagnet thickness is not. Consequently, tight\ncontrol over the nanomagnet thickness must be maintained for stochastic\ncomputing applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical Kerr Effect in Graphene: Theoretical Analysis of the Optical\n  Heterodyne Detection Technique: Graphene is an atomically thin two-dimensional material demonstrating strong\noptical nonlinearities including harmonics generation, four wave mixing, Kerr\nand other nonlinear effects. In this paper we theoretically analyze the optical\nheterodyne detection (OHD) technique of measuring the optical Kerr effect (OKE)\nin two-dimensional crystals and show how to relate the quantities measured in\nsuch experiments with components of the third-order conductivity tensor\n$\\sigma^{(3)}_{\\alpha\\beta\\gamma\\delta}(\\omega_1,\\omega_2,\\omega_3)$ of the\ntwo-dimensional crystal. Using results of a recently developed quantum theory\nof the third-order nonlinear electrodynamic response of graphene we analyze the\nfrequency, charge carrier density, temperature and other dependencies of the\nOHD-OKE response of this material. We compare our results with a recent OHD-OKE\nexperiment in graphene and find good agreement between the theory and\nexperiment.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Decay and Frequency Shift of Inter and Intravalley Phonons in Graphene\n  -Dirac Cone Migration-: By considering analytical expressions for the self-energies of intervalley\nand intravalley phonons in graphene, we describe the behavior of D, 2D, and\nD$'$ Raman bands with changes in doping ($\\mu$) and light excitation energy\n($E_L$). Comparing the self-energy with the observed $\\mu$ dependence of the 2D\nbandwidth, we estimate the wavevector $q$ of the constituent intervalley phonon\nat $\\hbar vq\\simeq E_L/1.6$ ($v$ is electron's Fermi velocity) and conclude\nthat the self-energy makes a major contribution (60%) to the dispersive\nbehavior of the D and 2D bands. The estimation of $q$ is based on an image of\nshifted Dirac cones in which the resonance decay of a phonon satisfying $q >\n\\omega/v$ ($\\omega$ is the phonon frequency) into an electron-hole pair is\nsuppressed when $\\mu < (vq-\\omega)/2$. We highlight the fact that the decay of\nan intervalley (and intravalley longitudinal optical) phonon with $q=\\omega/v$\nis strongly suppressed by electron-phonon coupling at an arbitrary $\\mu$. This\nfeature is in contrast to the divergent behavior of an intravalley transverse\noptical phonon, which bears a close similarity to the polarization function\nrelevant to plasmons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Structure and energetics of carbon, hexagonal boron nitride and\n  carbon/hexagonal boron nitride single-layer and bilayer nanoscrolls: Single-layer and bilayer carbon and hexagonal boron nitride nanoscrolls as\nwell as nanoscrolls made of bilayer graphene/hexagonal boron nitride\nheterostructure are considered. Structures of stable states of the\ncorresponding nanoscrolls prepared by rolling single-layer and bilayer\nrectangular nanoribbons are obtained based on the analytical model and\nnumerical calculations. The lengths of nanoribbons for which stable and\nenergetically favorable nanoscrolls are possible are determined. Barriers to\nrolling of single-layer and bilayer nanoribbons into nanoscrolls and barriers\nto nanoscroll unrolling are calculated. Based on the calculated barriers\nnanoscroll lifetimes in the stable state are estimated. Elastic constants for\nbending of graphene and hexagonal boron nitride layers used in the model are\nfound by density functional theory calculations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bismuth antiphase domain wall: A three-dimensional manifestation of the\n  Su-Schrieffer-Heeger model: The Su, Schrieffer and Heeger (SSH) model, describing the soliton excitations\nin polyacetylene due to the formation of antiphase domain walls (DW) from the\nalternating bond pattern, has served as a paradigmatic example of\none-dimensional (1D) chiral topological insulators. While the SSH model has\nbeen realized in photonic and plasmonic systems, there have been limited\nanalogues in three-dimensional (3D) electronic systems, especially regarding\nthe formation of antiphase DWs. Here, we propose that pristine bulk Bi, in\nwhich the dimerization of $(111)$ atomic layers renders alternating covalent\nand van der Waals bonding within and between successive $(111)$ bilayers,\nrespectively, serves as a 3D analogue of the SSH model. First, we confirm that\nthe two dimerized Bi structures belong to different Zak phases of 0 and $\\pi$\nby considering the parity eigenvalues and Wannier charge centers, while the\npreviously reported bulk topological phases of Bi remain invariant under the\ndimerization reversal. Next, we demonstrate the existence of topologically\nnon-trivial $(111)$ and trivial $(11\\bar{2})$ DWs in which the number of in-gap\nDW states (ignoring spin) is odd and even respectively, and show how this\ncontrols the interlinking of the Zak phases of the two adjacent domains.\nFinally, we derive general criteria specifying when a DW of arbitrary\norientation exhibits a $\\pi$ Zak phase based on the flip of parity eigenvalues.\nAn experimental realization of dimerization in Bi and the formation of DWs may\nbe achieved via intense femtosecond laser excitations that can alter the\ninteratomic forces and bond lengths.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Field electron emission theory (October 2016),v2: This document provides an updated account of material originally presented in\ntwo field electron emission (FE) tutorial lectures given at the 2016 Young\nResearchers' School in Vacuum Micro/Nano Electronics, held in Saint-Petersburg\nin October 2016. The aim of the tutorial lectures was to set out modern\nversions of some of the basics of mainstream FE theory. This paper indicates,\nin some depth, the scope, structure and content of the tutorials, and also\nwhere some of the related published material can be found.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Phonon-bottleneck enhanced magnetic hysteresis in a molecular paddle\n  wheel complex of Ru$_2^{5+}$: The ruthenium based molecular magnet\n[Ru$_2$(D(3,5-Cl$_2$Ph)F)$_4$Cl(0.5H$_2$O)$\\cdotp$C$_6$H$_{14}$] (hereafter\nRu$_2$) behaves as a two-level system at sufficiently low temperatures. The\nauthors performed spin detection by means of single-crystal measurements and\nobtained magnetic hysteresis loops around zero bias as a function of field\nsweeping rate. Compared to other molecular systems, Ru$_2$ presents an enhanced\nirreversibility as shown by ``valleys'' of negative differential susceptibility\nin the hysteresis curves. Simulations based on phonon bottleneck model are in\ngood qualitative agreement and suggest an abrupt spin reversal combined with\ninsufficient thermal coupling between sample and cryostat phonon bath.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin Transfer Torque and Electric Current in Helical Edge States in\n  Quantum Spin Hall Devices: We study the dynamics of a quantum spin Hall edge coupled to a magnet with\nits own dynamics. Using spin transfer torque principles, we analyze the\ninterplay between spin currents in the edge state and dynamics of the axis of\nthe magnet, and draw parallels with circuit analogies. As a highlighting\nfeature, we show that while coupling to a magnet typically renders the edge\nstate insulating by opening a gap, in the presence of a small potential bias,\nspin-transfer torque can restore perfect conductance by transferring angular\nmomentum to the magnet. In the presence of interactions within the edge state,\nwe employ a Luttinger liquid treatment to show that the edge, when subject to a\nsmall voltage bias, tends to form a unique dynamic rotating spin wave state\nthat naturally couples into the dynamics of the magnet. We briefly discuss\nrealistic physical parameters and constraints for observing this interplay\nbetween quantum spin Hall and spin-transfer torque physics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin Properties of Low Density One-Dimensional Wires: We report conductance measurements of a ballistic one-dimensional (1D) wire\ndefined in the lower two-dimensional electron gas of a GaAs/AlGaAs double\nquantum well. At low temperatures there is an additional structure at\n$0.7(2e^2/h)$ in the conductance, which tends to $e^2/h$ as the electron\ndensity is decreased. We find evidence for complete spin polarization in a\nweakly disorderd 1D wire at zero magnetic field through the observation of a\nconductance plateau at $e^2/h$, which strengthens in an in-plane magnetic field\nand disappears with increasing electron density. In all cases studied, with\nincreasing temperature structure occurs at $0.6(2e^2/h)$. We suggest that the\n0.7 structure is a many-body spin state excited out of, either the\nspin-polarized electron gas at low densities, or the spin-degenerate electron\ngas at high densities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin current generation due to differential rotation: We study nonequilibrium spin dynamics in differentially rotating systems,\nderiving an effective Hamiltonian for conduction electrons in the comoving\nframe. In contrast to conventional spin current generation mechanisms that\nrequire vorticity, our theory describes spins and spin currents arising from\ndifferentially rotating systems regardless of vorticity. We demonstrate the\ngeneration of spin currents in differentially rotating systems, such as liquid\nmetals with Taylor-Couette flow. Our alternative mechanism will be important in\nthe development of nanomechanical spin devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Wide-Band Tuneability, Nonlinear Transmission, and Dynamic\n  Multistability in SQUID Metamaterials: Superconducting metamaterials comprising rf SQUIDs (Superconducting QUantum\nInterference Devices) have been recently realized and investigated with respect\nto their tuneability, permeability and dynamic multistability properties. These\nproperties are a consequence of intrinsic nonlinearities due to the sensitivity\nof the superconducting state to external stimuli. SQUIDs, made of a\nsuperconducting ring interrupted by a Josephson junction, possess yet another\nsource of nonlinearity, which makes them widely tuneable with an applied dc\ndlux. A model SQUID metamaterial, based on electric equivalent circuits, is\nused in the weak coupling approximation to demonstrate the dc flux tuneability,\ndynamic multistability, and nonlinear transmission in SQUID metamaterials\ncomprising non-hysteretic SQUIDs. The model equations reproduce the\nexperimentally observed tuneability patterns, and predict tuneability with the\npower of an applied ac magnetic magnetic field. Moreover, the results indicate\nthe opening of nonlinear frequency bands for energy transmission through SQUID\nmetamaterials, for sufficiently strong ac fields.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Kitaev spin models from topological nanowire networks: We show that networks of topological nanowires can realize the physics of\nexactly solvable Kitaev spin models with two-body interactions. This connection\narises from the description of the low-energy theory of both systems in terms\nof a tight-binding model of Majorana modes. In Kitaev spin models the Majorana\ndescription provides a convenient representation to solve the model, whereas in\nan array of topological nanowires it arises, because the physical Majorana\nmodes localized at wire ends permit tunnelling between wire ends and across\ndifferent Josephson junctions. We explicitly show that an array of junctions of\nthree wires -- a setup relevant to topological quantum computing with nanowires\n-- can realize the Yao-Kivelson model, a variant of Kitaev spin models on a\ndecorated honeycomb lattice. Translating the results from the latter, we show\nthat the network can be constructed to give rise to collective states\ncharacterized by Chern numbers \\nu = 0, +/-1 and +/-2, and that defects in an\narray can be associated with vortex-like quasi-particle excitations. Finally,\nwe analyze the stability of the collective states as well as that of the\nnetwork as a quantum information processor. We show that decoherence inducing\ninstabilities, be them due to disorder or phase fluctuations, can be understood\nin terms of proliferation of the vortex-like quasi-particles.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dissipation in graphene and nanotube resonators: Different damping mechanisms in graphene nanoresonators are studied: charges\nin the substrate, ohmic losses in the substrate and the graphene sheet,\nbreaking and healing of surface bonds (Velcro effect), two level systems,\nattachment losses, and thermoelastic losses. We find that, for realistic\nstructures and contrary to semiconductor resonators, dissipation is dominated\nby ohmic losses in the graphene layer and metallic gate. An extension of this\nstudy to carbon nanotube-based resonators is presented.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Disorder induced Coulomb gaps in graphene constrictions with different\n  aspect ratios: We present electron transport measurements on lithographically defined and\netched graphene nanoconstrictions with different aspect ratios including\ndifferent lengths (L) and widths (W). A roughly length-independent disorder\ninduced effective energy gap can be observed around the charge neutrality\npoint. This energy gap scales inversely with the width even in regimes where\nthe length of the constriction is smaller than its width (L<W). In very short\nconstrictions, we observe both resonances due to localized states or charged\nislands and an elevated overall conductance level (0.1-1e2/h), which is\nstrongly length-dependent in the gap region. This makes very short graphene\nconstrictions interesting for highly transparent graphene tunneling barriers.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Generation of hyper-entangled photon pairs in coupled microcavities: We propose and theoretically analyze a new scheme for generating\nhyper-entangled photon pairs in a system of polaritons in coupled planar\nmicrocavities. Starting from a microscopic model, we evaluate the relevant\nparametric scattering processes and numerically simulate the phonon-induced\nnoise background under continuous-wave excitation. Our results show that,\ncompared to other polariton entanglement proposals, our scheme enables the\ngeneration of photon pairs that are entangled in both path and polarization\ndegrees of freedom, and simultaneously leads to a strong reduction of the\nphotoluminesence noise background. This can significantly improve the fidelity\nof the entangled photon pairs under realistic experimental conditions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Observation of drift and diffusion processes in Ti/TiOx/Ti memristive\n  devices prepared by local anodic oxidation: We demonstrate that memristive devices can be fabricated by tip-induced\noxidation of thin metallic films using atomic force microscope. Electrical\nmeasurements of such prepared Ti/TiOx/Ti test structures confirmed their\nmemristive behavior and inferred diffusion of oxygen vacancies in the TiOx\nbarrier. Consequent Kelvin probe force microscopy studies provided evidence for\nthe diffusion, as well as for expected oxygen vacancy drift. Time evolution of\nthe space distribution of the vacancies due to the diffusion process revealed\nminute-scale (at least) retention times of the devices. The work presents\ntechnology alternative for fabrication of memristive nanodevices in geometry\nfavouring advantageous scanning probe microscopy studies of their in-barrier\nprocesses, as well as widely utilizable approach to search for novel oxide\nmaterials for perspective memristive applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Localized Many-Particle Majorana Modes with Vanishing Time-Reversal\n  Symmetry Breaking in Double Quantum Dots: We introduce the concept of spinful many-particle Majorana modes with local\nodd operator products, thereby preserving their local statistics. We consider a\nsuperconductor-double-quantum-dot system where these modes can arise with\nnegligible Zeeman splitting when Coulomb interactions are present. We find a\nreverse Mott-insulator transition, where the even- and odd-parity bands become\ndegenerate. Above this transition, Majorana operators move the system between\nthe odd-parity ground state, associated with elastic cotunneling, and the\neven-parity ground state, associated with crossed Andreev reflection. These\nMajorana modes are described in terms of one, three, and five operator\nproducts. Parity conservation results in a 4% periodic supercurrent in the even\nstate and no supercurrent in the odd state.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anisotropic RKKY interaction in spin polarized graphene: We study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction in the presence\nof spin polarized two dimensional Dirac fermions. We show that a spin\npolarization along the z-axis mediates an anisotropic interaction which\ncorresponds to a XXZ model interaction between two magnetic moments. For\nundoped graphene, while the $x$ part of interaction keeps its constant\nferromagnetic sign, its $z$ part oscillates with the distance of magnetic\nimpurities, $R$. A finite doping causes that both parts of the interaction\noscillate with $R$. We explore a beating pattern of oscillations of the RKKY\ninteraction along armchair and zigzag lattice directions, which occurs for some\ncertain values of the chemical potential. The two characteristic periods of the\nbeating are determined by inverse of the difference and the sum of the chemical\npotential and the spin polarization.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Superconducting insulators and localization of Cooper pairs: Rapid miniaturization of electronic devices and circuits demands profound\nunderstanding of fluctuation phenomena at the nanoscale. Superconducting\nnanowires -- serving as important building blocks for such devices -- may\nseriously suffer from fluctuations which tend to destroy long-range order and\nsuppress superconductivity. In particular, quantum phase slips (QPS)\nproliferating at low temperatures may turn a quasi-one-dimensional\nsuperconductor into a resistor or an insulator. Here, we introduce a physical\nconcept of QPS-controlled localization of Cooper pairs that may occur even in\nuniform nanowires without any dielectric barriers being a fundamental\nmanifestation of the flux-charge duality in superconductors. We demonstrate --\nboth experimentally and theoretically -- that deep in the \"insulating\" state\nsuch nanowires actually exhibit non-trivial superposition of superconductivity\nand weak Coulomb blockade of Cooper pairs generated by quantum tunneling of\nmagnetic fluxons across the wire.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strain induced mobility modulation in single-layer MoS$_{2}$: In this paper the effect of biaxial and uniaxial strain on the mobility of\nsingle-layer MoS$_{2}$ for temperatures T $>$ 100 K is investigated. Scattering\nfrom intrinsic phonon modes, remote phonon and charged impurities are\nconsidered along with static screening. Ab-initio simulations are utilized to\ninvestigate the strain induced effects on the electronic bandstructure and the\nlinearized Boltzmann transport equation is used to evaluate the low-field\nmobility under various strain conditions. The results indicate that the\nmobility increases with tensile biaxial and tensile uniaxial strain along the\narmchair direction. Under compressive strain, however, the mobility exhibits a\nnon-monotonic behavior when the strain magnitude is varied. In particular, with\na relatively small compressive strain of 1% the mobility is reduced by about a\nfactor of two compared to the unstrained condition, but with a larger\ncompressive strain the mobility partly recovers such a degradation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effect of strain, thickness, and local surface environment on electron\n  transport properties of oxygen-terminated copper thin films: Electron transport is studied in surface oxidized single-crystal copper thin\nfilms with a thickness of up to 5.6 nm by applying density functional theory\nand density functional tight binding methods to determine electron transport\nproperties within the ballistic regime. The variation of the electron\ntransmission as a function of film thickness as well as the different\ncontributions to the overall electron transmission as a function of depth into\nthe the films is examined. Transmission at the oxidized copper film surfaces is\nfound to be universally low. Films with thickness greater than 2.7 nm exhibit a\nsimilar behavior in local transmission per unit area with depth from the film\nsurface; transmission per unit area initially increases rapidly and then\nplateaus at a depth of approximately 0.35-0.5 nm away from the surface,\ndependent on surface facet. Unstrained films tend to exhibit a higher\ntransmission per unit area than corresponding films under tensile strain.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interaction effects on a Majorana zero mode leaking into a quantum dot: We have recently shown [Phys. Rev. B {\\bf 89}, 165314 (2014)] that a\nnon--interacting quantum dot coupled to a one--dimensional topological\nsuperconductor and to normal leads can sustain a Majorana mode even when the\ndot is expected to be empty, \\emph{i.e.}, when the dot energy level is far\nabove the Fermi level of he leads. This is due to the Majorana bound state of\nthe wire leaking into the quantum dot. Here we extend this previous work by\ninvestigating the low--temperature quantum transport through an {\\it\ninteracting} quantum dot connected to source and drain leads and side--coupled\nto a topological wire. We explore the signatures of a Majorana zero--mode\nleaking into the quantum dot for a wide range of dot parameters, using a\nrecursive Green's function approach. We then study the Kondo regime using\nnumerical renormalization group calculations. We observe the interplay between\nthe Majorana mode and the Kondo effect for different dot-wire coupling\nstrengths, gate voltages and Zeeman fields. Our results show that a \"0.5\"\nconductance signature appears in the dot despite the interplay between the\nleaked Majorana mode and the Kondo effect. This robust feature persists for a\nwide range of dot parameters, even when the Kondo correlations are suppressed\nby Zeeman fields and/or gate voltages. The Kondo effect, on the other hand, is\nsuppressed by both Zeeman fields and gate voltages. We show that the zero--bias\nconductance as a function of the magnetic field follows a well--known\nuniversality curve. This can be measured experimentally, and we propose that\nthe universal conductance drop followed by a persistent conductance of\n$0.5\\,e^2/h$ is evidence of the presence of Majorana--Kondo physics. These\nresults confirm that this \"0.5\" Majorana signature in the dot remains even in\nthe presence of the Kondo effect.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Supercurrent carried by non-equlibrium quasiparticles in a multiterminal\n  Josephson junction: We theoretically study coherent multiple Andreev reflections in a biased\nthree-terminal Josephson junction. We demonstrate that the direct current\nflowing through the junction consists of supercurrent components when the bias\nvoltages are commensurate. This dissipationless current depends on the phase in\nthe superconducting leads and stems from the Cooper pair transfer processes\ninduced by non-local Andreev reflections of the quasiparticles originating from\nthe superconducting leads. We identify supercurrent-enhanced lines in the\ncurrent and conductance maps of the recent measurement [Y. Cohen, et al., PNAS\n115, 6991 (2018)] on a nanowire Josephson junction and show that the magnitude\nof the phase-dependent current components is proportional to the junction\ntransparency with the power corresponding to the component order.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Gate-tuned quantum oscillations of topological surface states in\n  beta-Ag2Te: We report the strong experimental evidence of the existence of topological\nsurface states with large electric field tunability and mobility in beta-Ag2Te.\nPronounced 2D SdH oscillations have been observed in beta-Ag2Te nanoplates. A\nBerry phase is determined to be near pi using the Landau level fan diagram for\na relatively wide nanoplate while the largest electric field ambipolar effect\nin topological insulator so far (~ 2500%) in a narrow nanoplate. The pi Berry\nphase and the evolution of quantum oscillations with gate voltage (Vg) in the\nnanoplates strongly indicate the presence of topological surface states in\nbeta-Ag2Te. Moreover, the mobility of the narrow Ag2Te nanoplate is ~ 3x10^4\ncm^2s^-1V^-1 when the Fermi level is near the Dirac point. The realization of\ntopological surface states with large electrical tunability and high mobility\nindicates that beta-Ag2Te is a promising topological insulator for fundamental\nstudies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Impurity screening and stability of Fermi arcs against Coulomband\n  magnetic scattering in a Weyl monopnictide: We present a quasiparticle interference study of clean and Mn surface-doped\nTaAs, a prototypical Weyl semimetal, to test the screening properties as well\nas the stability of Fermi arcs against Coulomb and magnetic scattering.\nContrary to topological insulators, the impurities are effectively screened in\nWeyl semimetals. The adatoms significantly enhance the strength of the signal\nsuch that theoretical predictions on the potential impact of Fermi arcs can be\nunambiguously scrutinized. Our analysis reveals the existence of three\nextremely short, previously unknown scattering vectors. Comparison with theory\ntraces them back to scattering events between large parallel segments of\nspin-split trivial states, strongly limiting their coherence. In sharp contrast\nto previous work [R. Batabyal et al., Sci. Adv. 2, e1600709 (2016)], where\nsimilar but weaker subtle modulations were interpreted as evidence of\nquasiparticle interference originating from Femi arcs, we can safely exclude\nthis being the case. Overall, our results indicate that intra- as well as\ninter-Fermi arc scattering are strongly suppressed and may explain why-in spite\nof their complex multiband structure-transport measurements show signatures of\ntopological states in Weyl monopnictides.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "AC Josephson transport through interacting quantum dots: We investigate the AC Josephson current through a quantum dot with strong\nCoulomb interaction attached to two superconducting and one normal lead. To\nthis end, we perform a perturbation expansion in the tunneling couplings within\na diagrammatic real-time technique. The AC Josephson current is connected to\nthe reduced density matrix elements that describe superconducting correlations\ninduced on the quantum dot via proximity effect. We analyze the dependence of\nthe AC signal on the level position of the quantum dot, the charging energy,\nand the applied bias voltages.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Zero-bias anomaly and Kondo-assisted quasi-ballistic 2D transport: Nonequilibrium transport measurements in mesoscopic quasi-ballistic 2D\nelectron systems show an enhancement in the differential conductance around the\nFermi energy. At very low temperatures, such a zero-bias anomaly splits,\nleading to a suppression of linear transport at low energies. We also observed\na scaling of the nonequilibrium characteristics at low energies which resembles\nelectron scattering by two-state systems, addressed in the framework of\ntwo-channel Kondo model. Detailed sample-to-sample reproducibility indicates an\nintrinsic phenomenon in unconfined 2D systems in the low electron-density\nregime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quiet SDS Josephson Junctions for Quantum Computing: Unconventional superconductors exhibit an order parameter symmetry lower than\nthe symmetry of the underlying crystal lattice. Recent phase sensitive\nexperiments on YBCO single crystals have established the d-wave nature of the\ncuprate materials, thus identifying unambiguously the first unconventional\nsuperconductor. The sign change in the order parameter can be exploited to\nconstruct a new type of s-wave - d-wave - s-wave Josephson junction exhibiting\na degenerate ground state and a double-periodic current-phase characteristic.\nHere we discuss how to make use of these special junction characteristics in\nthe construction of a quantum computer. Combining such junctions together with\na usual s-wave link into a SQUID loop we obtain what we call a `quiet' qubit\n--- a solid state implementation of a quantum bit which remains optimally\nisolated from its environment.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic states and ferromagnetic resonance in geometrically frustrated\n  arrays of multilayer ferromagnetic nanoparticles ordered on triangular\n  lattices: We present a theoretical investigation of magnetostatic interaction effects\nin geometrically frustrated arrays of anisotropic multilayer ferromagnetic\nnanoparticles arranged in different spatially configured systems with\ntriangular symmetry. We show that the interlayer magnetostatic interaction\nsignificantly expands the opportunities to create magnetically frustrated\nsystems. The effects of the magnetostatic interaction in magnetization reversal\nprocesses and the possibility to control the ferromagnetic resonance spectrum\nin such systems are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Rashba scattering in the low-energy limit: We study potential scattering in a two-dimensional electron gas with Rashba\nspin-orbit coupling in the limit that the energy of the scattering electron\napproaches the bottom of the lower spin-split band. Focusing on two\nspin-independent circularly symmetric potentials, an infinite barrier and a\ndelta-function shell, we show that scattering in this limit is qualitatively\ndifferent from both scattering in the higher spin-split band and scattering of\nelectrons without spin-orbit coupling. The scattering matrix is purely\noff-diagonal with both off-diagonal elements equal to one, and all angular\nmomentum channels contribute equally; the differential cross section becomes\nincreasingly peaked in the forward and backward scattering directions; the\ntotal cross section exhibits quantized plateaus. These features are independent\nof the details of the scattering potentials, and we conjecture them to be\nuniversal. Our results suggest that Rashba scattering in the low-energy limit\nbecomes effectively one-dimensional.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coulomb drag in quantum circuits: We study drag effect in a system of two electrically isolated quantum point\ncontacts (QPC), coupled by Coulomb interactions. Drag current exhibits maxima\nas a function of QPC gate voltages when the latter are tuned to the transitions\nbetween quantized conductance plateaus. In the linear regime this behavior is\ndue to enhanced electron-hole asymmetry near an opening of a new conductance\nchannel. In the non-linear regime the drag current is proportional to the shot\nnoise of the driving circuit, suggesting that the Coulomb drag experiments may\nbe a convenient way to measure the quantum shot noise. Remarkably, the\ntransition to the non-linear regime may occur at driving voltages substantially\nsmaller than the temperature.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Influence of structural deformations on the reentrant conductance\n  feature in semiconducting nanowires: Helical states can be measured through the observation of the reentrant\nbehaviour, which is a dip in the conductance probed in semiconducting nanowires\n(NWs) with strong spin-orbit coupling (SOC) under the presence of an external\nperpendicular magnetic field. We investigate the effects of deformations in the\nelectronic transport in NWs considering the coupling between different\ntransverse modes. Within this approach, we show that the dip in the conductance\nof a NW is affected by the presence of a local constriction. Moreover, we find\nthat the reentrant feature in the conductance can appear in NWs with a local\nexpansion of its radius, even in the absence of SOC and magnetic field.\nFurthermore, we develop a numerical approach to calculate transport properties,\nwhich is able to include the deformation and the coupling among several\nscattering channels.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron drift velocity control in GaAs-in-Al2O3 quantum wire transistor\n  structure due to the electron scattering rate alteration: Electron transport in the transistor structure based on thin undoped\nGaAs-in-Al2O3 quantum wire is simulated by ensemble Monte-Carlo method taking\ninto account electron scattering by the phonons and surface roughness. The\ninfluence of surface roughness height on electron drift velocity at 77 and 300\nK is investigated for the values of longitudinal electric field strength of 0.1\nand 1.0 kV/cm. A possibility of electron drift velocity control due to\nvariation of the bias applied to the gates, which results in the electron\nscattering rate alteration, is ascertained.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical control and decoherence of spin qubits in quantum dots: We discuss various methods of all-optical spin control in semiconductor\nquantum dots. We present different ways of rotating a single confined electron\nspin by optical coupling to a trion state. We also discuss a method for\ncontrolling the polarization of a confined exciton via a two-photon transition.\nFinally, we analyze the effect of phonon-induced decoherence on the fidelity of\nthese optical spin control protocols.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic Conduction in Short DNA Wires: A strict method is used to calculate the current-voltage characteristics of a\ndouble-stranded DNA. A more reliable model considering the electrostatic\npotential drop along an individual DNA molecular wire between the contacts is\nconsidered and the corresponding Green's Function is obtained analytically\nusing Generating Function method, which avoids difficult numerical evaluations.\nThe obtained results indicate that the electrostatic drop along the wire always\nincreases the conductor beyond the threshold than without considering it, which\nis in agreement with recent experiments. The present method can also be used to\ncalculate the current-voltage characteristics for other molecular wires of\narbitrary length.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Exceptional rings protected by emergent symmetry for mechanical systems: We propose mechanical systems, described by Newton's equation of motion, as\nsuited platforms for symmetry protection of non-Hermitian topological\ndegeneracies. We point out that systems possess emergent symmetry, which is a\nunique properties of mechanical systems. Because of the emergent symmetry, in\ncontrast to other systems, fine-tuning of parameters (e.g., gain and loss) is\nnot required to preserve the symmetry protecting exceptional rings in two\ndimensions. The presence of symmetry-protected exceptional rings (SPERs) in two\ndimensions is numerically demonstrated for a mechanical graphene with friction.\nFurthermore, classification of symmetry-protected non-Hermitian degeneracies is\naddressed by taking into account the above special characteristics of\nmechanical systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-equilibrium dynamics in coupled quantum dots: The aim of this work is to study the non-equilibrium dynamics of electrons in\na coupled quantum well pair. To achieve this aim, we consider a non-symmetric\ndistribution of electrons in a double quantum well. We derive the nonlinear\ndynamical evolution of the carrier wave functions considering electron-phonon\ninteractions and a time-dependent Hartree potential in multielectron quantum\ndots. We show the possibility of having an electrostatic trap for part of the\nelectrons which are injected into one of the quantum wells.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "All epitaxial self-assembly of vertically-confined silicon color centers\n  using ultra-low temperature epitaxy: Silicon-based color centers (SiCCs) have recently emerged as a source of\nquantum light that could be well combined with existing telecom-based Si\nPhotonics platforms. However, considering the current SiCC fabrication\nprocesses, deterministic control over the vertical emitter position is\nimpossible due to the stochastic nature of the ion implantation deployed for\ncolor center formation. To bypass this bottleneck towards high-yield\nintegration, we demonstrate an entirely different creation method for various\nSiCCs, that relies solely on the epitaxial growth of Si and C-doped Si at\nuntypically low temperatures in a pristine growth environment. Careful\nadjustment to the SiCC's thermal budget allows the emitters to be confined\nwithin a layer thickness of less than 1 nm embedded at an arbitrary vertical\nposition within a highly crystalline Si matrix. Depending on the SiCC layer\ngrowth conditions and doping, different types of color centers, such as W\ncenters, T centers, or G'-centers can be created, some of which are\nparticularly promising as Si-based single photon sources and for spin-photon\ninterfaces. We show that the zero-phonon emission from G'-center ensembles can\nbe conveniently tuned by changing the C-doping concentration, characterized by\na systematic wavelength shift and significant linewidth narrowing towards low\nemitter densities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic nanoparticle sensing: decoupling the magnetization from the\n  excitation field: Remote sensing of magnetic nanoparticles has exciting applications for\nmagnetic nanoparticle hyperthermia and molecular detection. We introduce,\nsimulate, and experimentally demonstrate an innovation---a sensing coil that is\ngeometrically decoupled from the excitation field---for magnetic nanoparticle\nspectroscopy that increases the flexibility and capabilities of remote\ndetection. The decoupling enhances the sensitivity absolutely; to small amounts\nof nanoparticles, and relatively; to small changes in the nanoparticle\ndynamics. We adapt a previous spectroscopic method that measures the relaxation\ntime of nanoparticles and demonstrate a new measurement of nanoparticle\ntemperature that could potentially be used concurrently during hyperthermia.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ground state correlations in a trapped quasi one-dimensional Bose Gas: We review the basic concepts of a non-equilibrium kinetic theory of a trapped\nbosonic gas. By extending the successful mean-field concept of the\nGross-Pitaevskii equation with the effects of non-local, two particle quantum\ncorrelations, one obtains a renormalized binary interaction and allows for the\ndynamic establishment of non-classical many-particle quantum correlations.\nThese concepts are illustrated by self-consistent numerical calculations of the\nfirst and second order ground state quantum correlations of a harmonically\ntrapped, quasi one-dimensional bosonic gas. We do find a strong suppression of\nthe density fluctuations or, in other words, an enhanced number squeezing with\ndecreasing particle density.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Unconventional Bloch-Gr\u00fcneisen scattering in hybrid Bose-Fermi\n  systems: We report on the novel mechanism of electron scattering in hybrid Bose-Fermi\nsystems consisting of a two-dimensional electron gas in the vicinity of an\nexciton condensate: We show that a pair-of-bogolons--mediated scattering proves\nto be dominating over the conventional acoustic phonon channel and over the\nsingle-bogolon scattering, even if the screening is taken into account. We\ndevelop a microscopic theory of this effect, focusing on GaAs and MoS$_2$\nmaterials, and find the principal temperature dependence of resistivity,\ndistinct from the conventional phonon--mediated processes. Further, we\nscrutinize parameters and suggest a way to design composite samples with\npredefined electron mobilities and propose a mechanism of electron pairing for\nsuperconductivity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ar+-sputtered Ge (001) surface nanostructuring at high implant\n  temperature: Ion sputtering induced nanoscale pattern formation on Ge (001) surface by 500\neV Ar+ bombardment has been investigated for a wide range of ion incidence\nangles at temperature of 300 deg.C. A fourfold symmetric topography forms in\nthe angular regime 0 - 65 deg. Above 65 deg, they show a remarkable transition\ninto highly regular one-dimensional (1D) asymmetric pattern, known as\nperpendicular mode ripples. In order to understand growth dynamics of both kind\nof patterns, we have investigated their temporal evolution as a function of ion\nfluence in a wide range from 1*10^{17} to 1*10^{20} ions cm-2. In addition, we\nstudy the effect of substrate rotation on Ge surface morphology in whole\nangular range. The four-fold symmetric patterns effect does not found to alter\ntheir symmetry, while the ripples degenerate into hole structure with a weak\nfourfold symmetric pattern. The origin of square topographies and their\nsymmetry independency on ion incident angle in the range 0 to 65 deg can be\nattributed to the growth process due to biased diffusion of vacancies arising\nfrom Ehrlich-Schwoebel barrier. Whereas, the ripple formation at grazing\nincidence angles indicates the dominance of curvature dependent surface\ninstability induced by the incident ion direction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "DFT modelling of the effect of strong magnetic field on Aniline molecule: Aniline is an organic compound with the stoichiometric expression\n$C_{6}H_{5}NH_{2}$; consisting of a phenyl structure attached to an amino\ngroup. It is colorless, but it slowly oxidizes and resinifies in air, giving a\nred-brown tint to aged samples. Until now, there are only few researches on\nAniline considering low magnetic fields. In this work, we study Aniline\nmolecule under different high magnetic fields using density functional theory\nmethods including independent particle and interacting particle approaches. We\nobtain charge density distrubitions, energy dispersions, dipol moments and\nforces as functions of position and magnetic field. Our numerical results show\nthat magnetic field affects electron density of the considered molecule. As a\nresult, it is observed that there are strong fluctuations in energy dispersion.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Energetics of metal slabs and clusters: the rectangle-box model: An expansion of energy characteristics of wide thin slab of thickness L in\npower of 1/L is constructed using the free-electron approximation and the model\nof a potential well of finite depth. Accuracy of results in each order of the\nexpansion is analyzed. Size dependences of the work function and electronic\nelastic force for Au and Na slabs are calculated. It is concluded that the work\nfunction of low-dimensional metal structure is always smaller that of\nsemi-infinite metal sample.\n  A mechanism for the Coulomb instability of charged metal clusters, different\nfrom Rayleigh's one, is discussed. The two-component model of a metallic\ncluster yields the different critical sizes depending on a kind of charging\nparticles (electrons or ions). For the cuboid clusters, the electronic spectrum\nquantization is taken into account. The calculated critical sizes of\nAg_{N}^{2-} and Au_{N}^{3-} clusters are in a good agreement with experimental\ndata. A qualitative explanation is suggested for the Coulomb explosion of\npositively charged Na_{\\N}^{n+} clusters at 3<n<5.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Voltage tunable quantum dot array by patterned Ge-nanowire based\n  metal-oxide-semiconductor (MOS) devices: Semiconductor quantum dots (QDs) are being regarded as the primary unit for a\nwide range of advanced and emerging technologies including electronics,\noptoelectronics, photovoltaics and biosensing applications as well as the\ndomain of q-bits based quantum information processing. Such QDs are suitable\nfor several novel device applications for their unique property of confining\ncarriers 3-dimensionally creating discrete quantum states. However, the\nrealization of such QDs in practice exhibits serious challenge regarding their\nfabrication in array with desired scalability and repeatability as well as\ncontrol over the quantum states at room temperature. In this context, the\ncurrent work reports the fabrication of an array of highly scaled Ge-nanowire\n(radius ~25 nm) based vertical metal-oxide-semiconductor devices that can\noperate as voltage tunable quantum dots at room temperature. The electrons in\nsuch nanowire experience a geometrical confinement in the radial direction,\nwhereas, they can be confined axially by tuning the applied bias in order to\nmanipulate the quantum states. Such quantum confinement of electrons has been\nconfirmed from the step-like responses in the room temperature\ncapacitance-voltage (C-V) characteristics at relatively low frequency (200\nkHz). Each of such steps has observed to encompass convolution of the quantized\nstates occupying ~6 electronic charges. The details of such carrier confinement\nare analyzed in the current work by theoretically modeling the device transport\nproperties based on non-equilibrium Green's function (NEGF) formalism.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dirac Spin-Orbit Torques at the Surface of Topological Insulators: We address the nature of spin-orbit torques at the magnetic surfaces of\ntopological insulators, using both Kubo formula and Keldysh formalism. Through\nthe analysis of the derived spin-charge equations, we find that the so-called\nDirac torques possess a different symmetry compared to their Rashba\ncounterpart, as well as a high anisotropy as a function of the magnetization\ndirection. In particular, the damping torque vanishes when the magnetization\nlies in the plane of the topological insulator surface. This peculiarity has\nimportant consequences in terms of magnetization dynamics and switching, as\ndemonstrated numerically via a macrospin model.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Zero-field Time Correlation Functions of Four Classical Heisenberg Spins\n  on a Ring: A model relevant for the study of certain molecular magnets is the ring of\nN=4 classical spins with equal near-neighbor isotropic Heisenberg exchange\ninteractions. Assuming classical Heisenberg spin dynamics, we solve explicitly\nfor the time evolution of each of the spins. Exact triple integral\nrepresentations are derived for the auto, near-neighbor, and\nnext-nearest-neighbor time correlation functions for any temperature. At\ninfinite temperature, the correlation functions are reduced to quadrature. We\nthen evaluate the Fourier transforms of these functions in closed form, which\nare double integrals. At low temperatures, the Fourier transform functions\nexplicitly demonstrate the presence of magnons. Our exact results for the\ninfinite temperature correlation functions in the long-time asymptotic limit\ndiffer qualitatively from those obtained assuming diffusive spin dynamics.\nWhether such explicitly non-hydrodynamic behavior would be maintained for\nlarge-N rings is discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interplay of spin-orbit coupling and Coulomb interaction in ZnO-based\n  electron system: Spin-orbit coupling (SOC) is pivotal for various fundamental spin-dependent\nphenomena in solids and their technological applications. In semiconductors,\nthese phenomena have been so far studied in relatively weak electron-electron\ninteraction regimes, where the single electron picture holds. However, SOC can\nprofoundly compete against Coulomb interaction, which could lead to the\nemergence of unconventional electronic phases. Since SOC depends on the\nelectric field in the crystal including contributions of itinerant electrons,\nelectron-electron interactions can modify this coupling. Here we demonstrate\nthe emergence of SOC effect in a high-mobility two-dimensional electron system\nin a simple band structure MgZnO/ZnO semiconductor. This electron system\nfeatures also strong electron-electron interaction effects. By changing the\ncarrier density with Mg-content, we tune the SOC strength and achieve its\ninterplay with electron-electron interaction. These systems pave a way to\nemergent spintronic phenomena in strong electron correlation regime and to the\nformation of novel quasiparticles with the electron spin strongly coupled to\nthe density.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermoelectric response of fractional quantized Hall and re-entrant\n  insulating states in the N=1 Landau level: Detailed measurements of the longitudinal thermopower of two-dimensional\nelectrons in the first excited Landau level are reported. Clear signatures of\nnumerous fractional quantized Hall states, including those at $\\nu = 5/2$ and\n7/3, are observed in the magnetic field and temperature dependence of the\nthermopower. An abrupt collapse of the thermopower is observed below about $T=\n40$ mK at those filling factors where re-entrant insulating electronic states\nhave been observed in conventional resistive transport studies. The thermopower\nobserved at $\\nu = 5/2$ is discussed in the context of recent theories which\nincorporate non-abelian quasiparticle exchange statistics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Conductance saturation in a series of highly transmitting molecular\n  junctions: Understanding the properties of electronic transport across metal-molecule\ninterfaces is of central importance for controlling a large variety of\nmolecular-based devices such as organic light emitting diodes, nanoscale\norganic spin-valves and single-molecule switches. One of the primary\nexperimental methods to reveal the mechanisms behind electronic transport\nthrough metal-molecule interfaces is the study of conductance as a function of\nmolecule length in molecular junctions. Previous studies focused on transport\ngoverned either by tunneling or hopping, both at low conductance. However, the\nupper limit of conductance across molecular junctions has not been explored,\ndespite the great potential for efficient information transfer, charge\ninjection and recombination processes. Here, we study the conductance\nproperties of highly transmitting metal-molecule-metal interfaces, using a\nseries of single-molecule junctions based on oligoacenes with increasing\nlength. We find that the conductance saturates at an upper limit where it is\nindependent of molecule length. Furthermore, we show that this upper limit can\nbe controlled by the character of the orbital hybridization at the\nmetal-molecule interface. Using two prototype systems, in which the molecules\nare contacted by either Ag or Pt electrodes, we reveal two different origins\nfor the saturation of conductance. In the case of Ag-based molecular junctions,\nthe conductance saturation is ascribed to a competition between energy level\nalignment and level broadening, while in the case of Pt-based junctions, the\nsaturation is attributed to a band-like transport. The results are explained by\nan intuitive model, backed by ab-initio transport calculations. Our findings\nshed light on the mechanisms that constrain the conductance at the high\ntransmission limit, providing guiding principles for the design of highly\nconductive metal-molecule interfaces.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Rashba effect and magnetic field in quantum wires: We investigate the influence of a perpendicular magnetic field on the\nspectral and spin properties of a ballistic quasi-one-dimensional electron\nsystem with Rashba effect. The magnetic field strongly alters the spin-orbit\ninduced modification to the subband structure when the magnetic length becomes\ncomparable to the lateral confinement. A new subband-dependent energy splitting\nat k=0 is found which can be much larger than the Zeeman splitting. This is due\nto the breaking of a combined spin orbital-parity symmetry.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport phenomena in helical edge states interferometers. A Green's\n  function approach: We analyze the current and the shot-noise of an electron interferometer made\nof the helical edge states of a two-dimensional topological insulator within\nthe framework of non-equilibrium Green's functions formalism. We study in\ndetail setups with a single and with two quantum point contacts inducing\nscattering between the different edge states. We consider processes preserving\nthe spin as well as the effect of spin-flip scattering. In the case of a single\nquantum point contact, a simple test based on the shot-noise measurement is\nproposed to quantify the strength of the spin-flip scattering. In the case of\ntwo single point contacts with the additional ingredient of gate voltages\napplied within a finite-size region at the top and bottom edges of the sample,\nwe identify two type of interference processes in the behavior of the currents\nand the noise. One of such processes is analogous to that taking place in a\nFabry-P\\'erot interferometer, while the second one corresponds to a\nconfiguration similar to a Mach-Zehnder interferometer. In the helical\ninterferometer these two processes compete.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electrical transport between epitaxial manganites and carbon nanotubes: The possibility of performing spintronics at the molecular level may be\nrealized in devices that combine fully spin polarized oxides such as manganites\nwith carbon nanotubes. However, it is not clear whether electrical transport\nbetween such different material systems is viable. Here we show that the room\ntemperature conductance of manganite-nanotube-manganite devices is only half\nthe value recorded in similar palladium-nanotube-palladium devices.\nInterestingly, the former shows a pseudogap in the conductivity below the\nrelatively high temperature of 200 K. Our results suggest the possibility of\nnew spintronics heterostructures that exploit fully spin polarized sources and\ndrains.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "On the radiative lifetime of free-moving two-dimensional excitons: A simple microscopic mechanism explaining the linear dependence of the\nradiative lifetime of free-moving two-dimensional excitons on their effective\ntemperature is suggested. It is shown that there exists a characteristic\neffective temperature (of about few Kelvin) defined by the exciton-acoustic\nphonon interaction at which the radiative lifetime is minimal. Below this\ntemperature the lifetime starts to increase with decreasing temperature. The\ncorrespondence with previous theoretical and experimental results is discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Resonant dynamics of skyrmion lattices in thin film multilayers:\n  Localised modes and spin wave emission: The spectral signatures of magnetic skyrmions under microwave field\nexcitation are of fundamental interest and can be an asset for high frequency\napplications. These topological solitons can be tailored in multilayered thin\nfilms, but the experimental observation of their spin wave dynamics remains\nelusive, in particular due to large damping. Here, we study Pt/FeCoB/AlO$_x$\nmultilayers hosting dense and robust skyrmion lattices at room temperature with\nGilbert damping of $\\sim 0.02$. We use magnetic force microscopy to\ncharacterise their static magnetic phases and broadband ferromagnetic resonance\nto probe their high frequency response. Micromagnetic simulations reproduce the\nexperiments with accuracy and allow us to identify distinct resonant modes\ndetected in the skyrmion lattice phase. Low ($<$ 2 GHz) and intermediate\nfrequency ($2-8$ GHz) modes involve excitations localised to skyrmion edges in\nconjunction with precession of the uniform background magnetisation, while a\nhigh frequency ($>$ 12 GHz) mode corresponds to in-phase skyrmion core\nprecession emitting spin waves into uniform background with wavelengths in the\n50--80 nm range commensurate with the lattice structure. These findings could\nbe instrumental in the investigation of room temperature wave scattering and\nthe implementation of novel microwave processing schemes in reconfigurable\narrays of solitons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ideal Chern bands are Landau levels in curved space: We prove that all the criteria proposed in the literature to identify a Chern\nband hosting exact fractional Chern insulating ground states, in fact, describe\nan equivalence with a lowest Landau level defined in curved space under a\nnon-uniform magnetic field. In addition, we design an operational test for the\nmost general instance of such lowest Landau level mapping, which only relies on\nthe computationally inexpensive evaluation of Bloch wavefunctions' derivatives.\nOur work clarifies the common origin of various Chern-idealness criteria,\nproves that these criteria exhaust all possible lowest Landau levels, and hints\nat classes of Chern bands that may posses interesting phases beyond Landau\nlevel physics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current-driven ferromagnetic resonance, mechanical torques and rotary\n  motion in magnetic nanostructures: We study theoretically the detection and possible utilization of electric\ncurrent-induced mechanical torques in ferromagnetic-normal metal\nheterostructures that are generated by spin-flip scattering or the absorption\nof transverse spin currents by a ferromagnet. To this end, we analyze the DC\nvoltage signals over a spin valve that is driven by an AC current. In agreement\nwith recent studies, this \"rectification\", measured as a function of AC\nfrequency and applied magnetic field, contains important information on the\nmagnetostatics and --dynamics. Subsequently, we show that the vibrations\nexcited by spin-transfer to the lattice can be detected as a splitting of the\nDC voltage resonance. Finally, we propose a concept for a spin-transfer-driven\nelectric nanomotor based on integrating metallic nanowires with carbon\nnanotubes, in which the current-induced torques generate a rotary motion.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Robust polaritons in magnetic monolayers of CrI3: We show that the regime of strong-light matter coupling with remarkable\nmagnetic properties can be realized in systems based on monolayers of chromium\ntriiodide (CrI3). This two-dimensional material combines the presence of\nferromagnetic ordering with the possibility of forming strongly-bound excitonic\ncomplexes even at room temperature. Using microscopic first-principle\ncalculations we reveal a rich spectrum of optical transitions, corresponding to\nboth Wannier- and Frenkel-type excitons, including those containing electrons\nwith a negative effective mass. We show that excitons of different\npolarizations efficiently hybridize with a photonic mode of a planar\nmicrocavity, and due to the peculiar selection rules polariton modes become\nwell resolved in circular polarizations. The combination of very strong optical\noscillator strength of excitons and cavity confinement leads to large values of\nthe Rabi splitting, reaching 35 meV for a single monolayer, and giant Zeeman\nsplitting between polariton modes of up to 20 meV. This makes CrI3 an excellent\nplatform for magnetopolaritonic applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Two-Dimensional Wide-Band-Gap II-V Semiconductors with a Dilated\n  Graphene-like Structure: Since the advent of graphene, two-dimensional (2D) materials become very\nattractive and there is growing interest to explore new 2D beyond graphene.\nHere, through density functional theory (DFT) calculations, we predict 2D\nwide-band-gap II-V semiconductor materials of M$_3$X$_2$ (M=Zn, Cd and X=N, P,\nAs) with a dilated graphene-like honeycomb structure. The structure features\nthat the group-V X atoms form two X-atomic planes symmetrically astride the\ncentering group-IIB M atomic plane. The 2D Zn$_3$N$_2$, Zn$_3$P$_2$, and\nZn$_3$As$_2$ are shown to have direct band gaps of 2.87, 3.81, and 3.55 eV,\nrespectively, and the 2D Cd$_3$N$_2$, Cd$_3$P$_2$, and Cd$_3$As$_2$ exhibit\nindirect band gaps of 2.74, 3.51, and 3.29 eV, respectively. Each of the six 2D\nmaterials is shown to have effective carrier (either hole or electron) masses\ndown to $0.03\\sim 0.05$ $m_0$. The structural stability and feasibility of\nexperimental realization of these 2D materials has been shown in terms of DFT\nphonon spectra and total energy comparison with related existing bulk\nmaterials. On the experimental side, there already are many similar\ntwo-coordinate structures of Zn and other transition metals in various organic\nmaterials, which can be considered to support our DFT prediction. Therefore,\nthese 2D semiconductors can enrich the family of 2D electronic materials and\nmay have promising potential for achieving novel transistors and optoelectronic\ndevices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dipole representation of half-filled Landau level: We introduce a variant of dipole representation for composite fermions in a\nhalf-filled Landau level, taking into account the symmetry under exchange of\nparticles and holes. This is implemented by a special constraint on composite\nfermion and composite hole degree of freedom (of an enlarged space), that makes\nthe resulting composite particle, dipole, a symmetric object. We study an\neffective Hamiltonian, that commutes with the constraint on the physical space,\nand fulfills the requirement for boost invariance on the Fermi level. The\ncalculated Fermi liquid parameter F2 is in a good agreement with numerical\ninvestigations in [Phys. Rev. Lett. 121, 147601 (2018)].",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Emergent topological fields and relativistic phonons within the\n  thermoelectricity in topological insulators: Topological edge states are predicted to be responsible for the high\nefficient thermoelectric response of topological insulators, currently the best\nthermoelectric materials. However, to explain their figure of merit the\ncoexistence of topological electrons, entropy and phonons can not be considered\nindependently. In a background that puts together electrodynamics and topology,\nthrough an expression for the topological intrinsic field, we treat\nrelativistic phonons within the topological surface showing their ability to\nmodulate the Berry curvature of the bands and then playing a fundamental role\nin the thermoelectric effect. Finally, we show how the topological insulators\nunder such relativistic thermal excitations keep time reversal symmetry\nallowing the observation of high figures of merit at high temperatures. The\nemergence of this new intrinsic topological field and other constraints are\nsuitable to have experimental consequences opening new possibilities of\nimproving the efficiency of this topological effect for their based technology.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "OLEDs as models for bird magnetoception: detecting electron spin\n  resonance in geomagnetic fields: Certain species of living creatures are known to orientate themselves in the\ngeomagnetic field. Given the small magnitude of approximately 48 {\\mu}T, the\nunderlying quantum mechanical phenomena are expected to exhibit coherence times\napproaching the millisecond regime. In this contribution, we show sensitivity\nof organic light-emitting diodes (OLEDs) to magnetic fields far below Earth's\nmagnetic field, suggesting that coherence times of the spins of charge-carrier\npairs in these devices can be similarly long. By electron paramagnetic\nresonance (EPR) experiments, a lower bound for the coherence time can be\nassessed directly. Moreover, this technique offers the possibility to determine\nthe distribution of hyperfine fields within the organic semiconductor layer. We\nextend this technique to a material system exhibiting both fluorescence and\nphosphorescence, demonstrating stable anticorrelation between optically\ndetected magnetic resonance (ODMR) spectra in the singlet (fluorescence) and\ntriplet (phosphorescence) channel. The experiments demonstrate the extreme\nsensitivity of OLEDs to both static as well as dynamic magnetic fields and\nsuggest that coherent spin precession processes of Coulombically bound electron\nspin pairs may play a crucial role in the magnetoreceptive ability of living\ncreatures.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Deflection of (anti)ferromagnetic skyrmions at heterochiral interfaces: Devising magnetic nanostructures with spatially heterogeneous\nDzyaloshinskii-Moriya interaction (DMI) is a promising pathway towards advanced\nconfinement and control of magnetic skyrmions in potential devices. Here we\ndiscuss theoretically how a skyrmion interacts with a heterochiral interface\nusing micromagnetic simulations and analytic arguments. We show that a\nheterochiral interface deflects the trajectory of ferromagnetic (FM) skyrmions,\nand that the extent of such deflection is tuned by the applied spin-polarized\ncurrent and the difference in DMI across the interface. Further, we show that\nthis deflection is characteristic for the FM skyrmion, and is completely absent\nin the antiferromagnetic (AFM) case. In turn, we reveal that the AFM skyrmion\nachieves much higher velocities than its FM counterpart, yet experiences far\nstronger confinement in nanoengineered heterochiral tracks, which reinforces\nAFM skyrmions as a favorable choice for skyrmion-based devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Excess electron screening of remote donors and mobility in modern\n  GaAs/AlGaAs herostructures: In modern GaAs/Al$_x$Ga$_{1-x}$As heterostructures with record high\nmobilities, a two-dimensional electron gas (2DEG) in a quantum well is provided\nby two remote donor $\\delta$-layers placed on both sides of the well. Each\n$\\delta$-layer is located within a narrow GaAs layer, flanked by narrow AlAs\nlayers which capture excess electrons from donors but leave each of them\nlocalized in a compact dipole atom with a donor. Still excess electrons can hop\nbetween host donors to minimize their Coulomb energy. As a result they screen\nthe random potential of donors dramatically. We numerically model the\npseudoground state of excess electrons at a fraction $f$ of filled donors and\nfind both the mobility and the quantum mobility limited by scattering on remote\ndonors as universal functions of $f$. We repeat our simulations for devices\nwith additional disorder such as interface roughness of the doping layers, and\nfind the quantum mobility is consistent with measured values. Thus, in order to\nincrease the quantum mobility this additional disorder should be minimized.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Large low-frequency resistance noise in chemical vapor deposited\n  graphene: We report a detailed investigation of resistance noise in single layer\ngraphene films on Si/SiO$_2$ substrates obtained by chemical vapor deposition\n(CVD) on copper foils. We find that noise in these systems to be rather large,\nand when expressed in the form of phenomenological Hooge equation, it\ncorresponds to Hooge parameter as large as $0.1 - 0.5$. We also find the\nvariation in the noise magnitude with the gate voltage (or carrier density) and\ntemperature to be surprisingly weak, which is also unlike the behavior of noise\nin other forms of graphene, in particular those from exfoliation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Robustness of Helical Edge States Under Edge Reconstruction: The helical edge states of time-reversal invariant two-dimensional\ntopological insulators are protected against backscattering in idealized\nmodels. In more realistic scenarios with a shallow confining potential at the\nsample boundary, additional strongly interacting edge states may arise, that\ncould interfere with the topological protection of edge conduction. We find\nthat interaction effects within the reconstructed edges are well described by\nthe Luttinger liquid model. While interactions between this Luttinger liquid\nand the helical edge states can in principle give rise to dynamical spin\npolarization and the breaking of time-reversal symmetry, we demonstrate that\nrandom spin-orbit coupling strongly suppresses such dynamical spin\npolarization, resulting in the persistence of near quantized edge conduction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anisotropy-assisted magnon condensation in ferromagnetic thin films: We theoretically demonstrate that adding an easy-axis magnetic anisotropy\nfacilitates magnon condensation in thin yttrium iron garnet (YIG) films.\nDipolar interactions in a quasi-equilibrium state stabilize room-temperature\nmagnon condensation in YIG. Even though the out-of-plane easy-axis anisotropy\ngenerally competes with the dipolar interactions, we show that adding such\nmagnetic anisotropy may even assist the generation of the magnon condensate\nelectrically via the spin transfer torque mechanism. We use analytical\ncalculations and micromagnetic simulations to illustrate this effect. Our\nresults may explain the recent experiment on Bi-doped YIG and open a pathway\ntoward applying current-driven magnon condensation in quantum spintronics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum criticality in a double quantum-dot system: We discuss the realization of the quantum-critical non-Fermi liquid state,\noriginally discovered within the two-impurity Kondo model, in double\nquantum-dot systems. Contrary to the common belief, the corresponding fixed\npoint is robust against particle-hole and various other asymmetries, and is\nonly unstable to charge transfer between the two dots. We propose an\nexperimental set-up where such charge transfer processes are suppressed,\nallowing a controlled approach to the quantum critical state. We also discuss\ntransport and scaling properties in the vicinity of the critical point.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Radio-frequency methods for Majorana-based quantum devices: fast charge\n  sensing and phase diagram mapping: Radio-frequency (RF) reflectometry is implemented in hybrid\nsemiconductor-superconductor nanowire systems designed to probe Majorana zero\nmodes. Two approaches are presented. In the first, hybrid nanowire-based\ndevices are part of a resonant circuit, allowing conductance to be measured as\na function of several gate voltages ~40 times faster than using conventional\nlow-frequency lock-in methods. In the second, nanowire devices are capacitively\ncoupled to a nearby RF single-electron transistor made from a separate\nnanowire, allowing RF detection of charge, including charge-only measurement of\nthe crossover from 2e inter-island charge transitions at zero magnetic field to\n1e transitions at axial magnetic fields above 0.6 T, where a topological state\nis expected. Single-electron sensing yields signal-to-noise exceeding 3 and\nvisibility 99.8% for a measurement time of 1 {\\mu}s.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Sign reversal of magnetoresistivity in massive nodal-line semimetals due\n  to Lifshitz transition of Fermi surface: Topological nodal-line semimetals offer an interesting research platform to\nexplore novel phenomena associated with its torus-shaped Fermi surface. Here,\nwe study magnetotransport in the massive nodal-line semimetal with spin-orbit\ncoupling and finite Berry curvature distribution which exists in many\ncandidates. The magnetic field leads to a deformation of the Fermi torus\nthrough its coupling to the orbital magnetic moment, which turns out to be the\nmain scenario of the magnetoresistivity (MR) induced by the Berry curvature\neffect. We show that a small deformation of the Fermi surface yields a positive\nMR $\\propto B^2$, different from the negative MR by pure Berry curvature effect\nin other topological systems. As the magnetic field increases to a critical\nvalue, a topological Lifshitz transition of the Fermi surface can be induced,\nand the MR inverts its sign at the same time. The temperature dependence of the\nMR is investigated, which shows a totally different behavior before and after\nthe Lifshitz transition. Our work uncovers a novel scenario of the MR induced\nsolely by the deformation of the Fermi surface and establishes a relation\nbetween the Fermi surface topology and the sign of the MR.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-Boltzmann classical correction to the velocity auto-correlation\n  function for isotropic scattering in two dimensions: The classical correction to the velocity auto-correlation function of\nnon-interacting particles due to memory effects, which are beyond the Boltzmann\nequation, is calculated both analytically and numerically for the case of\nisotropic scattering in two dimensions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetoelectric effects and valley controlled spin quantum gates in\n  transition metal dichalcogenide bilayers: In monolayer group-VI transition metal dichalcogenides (TMDC), charge\ncarriers have spin and valley degrees of freedom, both associated with magnetic\nmoments. On the other hand, the layer degree of freedom in multilayers is\nassociated with electrical polarization. Here, we show that TMDC bilayers offer\nan unprecedented platform to realize a strong coupling between the spin, layer\npseudospin, and valley degrees of freedom of holes. Such coupling not only\ngives rise to the spin Hall effect and spin circular dichroism in inversion\nsymmetric bilayer, but also leads to a variety of magnetoelectric effects\npermitting quantum manipulation of these electronic degrees of freedom.\nOscillating electric and magnetic fields can both drive the hole spin resonance\nwhere the two fields have valley-dependent interference, making possible a\nprototype interplay between the spin and valley as information carriers for\npotential valley-spintronic applications. We show how to realize quantum gates\non the spin qubit controlled by the valley bit.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interplay of valley, layer and band topology towards interacting quantum\n  phases in bilayer graphene moire superlattice: A Bilayer of semiconducting 2D electronic systems has long been a versatile\nplatform to study electronic correlation with tunable interlayer tunneling,\nCoulomb interactions and layer imbalance. In the natural graphite bilayer,\nBernal-stacked bilayer graphene (BBG), the Landau level gives rise to an\nintimate connection between the valley and layer. Adding a moire superlattice\npotential enriches the BBG physics with the formation of topological minibands,\npotentially leading to tunable exotic quantum transports. Here, we present\nmagnetotransport measurements of a high-quality bilayer graphene-hexagonal\nboron nitride (hBN) heterostructure. The zero-degree alignment generates a\nstrong moire superlattice potential for the electrons in BBG and the resulting\nLandau fan diagram of longitudinal and Hall resistance displays a Hofstadter\nbutterfly pattern with an unprecedented level of detail. We demonstrate that\nthe intricate relationship between valley and layer degrees of freedom controls\nthe topology of moire-induced bands, significantly influencing the energetics\nof interacting quantum phases in the BBG superlattice. We further observe\nsignatures of field-induced correlated insulators and clear fractional\nquantizations of interaction driven topological quantum phases, such as\nfractional Chern insulators. Our results highlight the BBG/hBN heterostructure\nas an ideal platform for studying the delicate interplay between topology and\nelectron correlation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mechanical Mixing in Nonlinear Nanomechanical Resonators: Nanomechanical resonators, machined out of Silicon-on-Insulator wafers, are\noperated in the nonlinear regime to investigate higher-order mechanical mixing\nat radio frequencies, relevant to signal processing and nonlinear dynamics on\nnanometer scales. Driven by two neighboring frequencies the resonators generate\nrich power spectra exhibiting a multitude of satellite peaks. This nonlinear\nresponse is studied and compared to $n^{th}$-order perturbation theory and\nnonperturbative numerical calculations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Surface Recombination Limited Lifetimes of Photoexcited Carriers in\n  Few-Layer Transition Metal Dichalcogenide MoS2: We present results on photoexcited carrier lifetimes in few-layer transition\nmetal dichalcogenide MoS2 using nondegenerate ultrafast optical pump-probe\ntechnique. Our results show a sharp increase of the carrier lifetimes with the\nnumber of layers in the sample. Carrier lifetimes increase from few tens of\npicoseconds in monolayer samples to more than a nanosecond in 10-layer samples.\nThe inverse carrier lifetime was found to scale according to the probability of\nthe carriers being present at the surface layers, as given by the carrier\nwavefunction in few layer samples, which can be treated as quantum wells. The\ncarrier lifetimes were found to be largely independent of the temperature and\nthe inverse carrier lifetimes scaled linearly with the photoexcited carrier\ndensity. These observations are consistent with defect-assisted carrier\nrecombination, in which the capture of electrons and holes by defects occurs\nvia Auger scatterings. Our results suggest that carrier lifetimes in few-layer\nsamples are surface recombination limited due to the much larger defect\ndensities at the surface layers compared to the inner layers.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quasiparticle diffusion based heating in superconductor tunneling\n  micro-coolers: In a hybrid Superconductor - Insulator - Normal metal tunnel junction biased\njust below the gap, the extraction of hot electrons out of the normal metal\nresults in electronic cooling effect. The quasiparticles injected in the\nsuperconductor accumulate near the tunnel interface, thus increasing the\neffective superconductor temperature. We propose a simple model for the\ndiffusion of excess quasiparticles in a superconducting strip with an\nadditional trap junction. This diffusion model has a complete analytic\nsolution, which depends on experimentally accessible parameters. We find that\nthe accumulated quasiparticles near the junction reduce the efficiency of the\ndevice. This study is also relevant to more general situations making use of\nsuperconducting tunnel junctions, as low temperature detectors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fingerprints of Qubit Noise in Transient Cavity Transmission: Noise affects the coherence of qubits and thereby places a bound on the\nperformance of quantum computers. We theoretically study a generic two-level\nsystem with fluctuating control parameters in a photonic cavity and find that\nbasic features of the noise spectral density are imprinted in the transient\ntransmission through the cavity. We obtain analytical expressions for generic\nnoise and proceed to study the cases of quasistatic, white and $1/f^{\\alpha}$\nnoise in more detail. Additionally, we propose a way of extracting the spectral\ndensity for arbitrary noise in a frequency band only bounded by the range of\nthe qubit-cavity detuning and with an exponentially decaying error due to\nfinite measurement times. Our results suggest that measurements of the\ntime-dependent transmission probability represent a novel way of extracting\nnoise characteristics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "From chaos to disorder: Statistics of the eigenfunctions of microwave\n  cavities: We study the statistics of the experimental eigenfunctions of chaotic and\ndisordered microwave billiards in terms of the moments of their spatial\ndistributions, such as the Inverse Participation Ratio (IPR) and\ndensity-density auto-correlation. A path from chaos to disorder is described in\nterms of increasing IPR. In the chaotic, ballistic limit, the data correspond\nwell with universal results from random matrix theory. Deviations from\nuniversal distributions are observed due to disorder induced localization, and\nfor the weakly disordered case the data are well-described by including finite\nconductance and mean free path contributions in the framework of nonlinear\nsigma models of supersymetry.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The next nearest neighbor effect on the 2D materials properties: In this work, the effect of introducing next nearest neighbor (NNN) hopping\nto the 2D materials was studied using the graphene 2D honeycomb two sublattice\nas an example. It is found that introducing NNN to the 2D materials removes the\nsymmetry around the Fermi level and shifts it, at a small value of NNN hopping.\nThis effect increases with increasing NNN hopping. If the NNN hopping becomes\ncompetitive with nearest neighbor (NN) hopping, the dispersion relations of the\n2D materials changes completely from NN hopping dispersion relations. The\nresults show that the 2D material sensitivity for NNN hopping effect is much\nlarger in the 2D honeycomb lattice than 2D square lattice. This is due to the\nfact that the number of NNN sites is equal to six, which is the double of NN\nsites in the 2D honeycomb lattice. Meanwhile, the number of NNN sites is equal\nto four which is equal to NN sites in 2D square lattice. We therefore conclude\nthat by changing the ratio between NNN and NN sites in the 2D lattice one can\ntune the sensitivity for NNN hopping effects.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dephasing effect promotes the appearance of quantized Hall plateaus: The quantum Hall effect (QHE) is a topologically protected phenomenon which\nhas been observed in various systems. In experiments, the size of Hall bar\ndevice to realize the QHE is generally much larger than the phase coherence\nlength, in which the quantum coherence of electrons is destroyed. Here, we\ntheoretically study the influence of dephasing effect on the quantized Hall\n(QH) plateaus. We find that the QH plateau disappears in perfectly quantum\ncoherent systems if the coupling between leads and central region is imperfect.\nThe Hall resistance is very large and strongly oscillates instead of presenting\nthe QH plateau in this case. However, by introducing the dephasing, the Hall\nresistance decreases and the QH plateau appears gradually. Similar results can\nalso be observed for the quantum anomalous Hall effect. Our results propose\nthat dephasing effect promotes the appearance of QH plateaus, which opens a new\ntopic of the dephasing effect on topological systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum magnetism and topological superconductivity in Yu-Shiba-Rusinov\n  chains: Chains of magnetic adatoms on superconductors have been discussed as\npromising systems for realizing Majorana end states. Here, we show that dilute\nYu-Shiba-Rusinov (YSR) chains are also a versatile platform for quantum\nmagnetism and correlated electron dynamics, with widely adjustable spin values\nand couplings. Focusing on subgap excitations, we derive an extended $t-J$\nmodel for dilute quantum YSR chains and use it to study the phase diagram as\nwell as tunneling spectra. We explore the implications of quantum magnetism for\nthe formation of a topological superconducting phase, contrasting it to\nexisting models assuming classical spin textures.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Giant Magnetoresistance Oscillations Induced by Microwave Radiation and\n  a Zero-Resistance State in a 2D Electron System with a Moderate Mobility: The effect of a microwave field in the frequency range from 54 to 140\n$\\mathrm{GHz}$ on the magnetotransport in a GaAs quantum well with AlAs/GaAs\nsuperlattice barriers and with an electron mobility no higher than $10^6$\n$\\mathrm{cm^2/Vs}$ is investigated. In the given two-dimensional system under\nthe effect of microwave radiation, giant resistance oscillations are observed\nwith their positions in magnetic field being determined by the ratio of the\nradiation frequency to the cyclotron frequency. Earlier, such oscillations had\nonly been observed in GaAs/AlGaAs heterostructures with much higher mobilities.\nWhen the samples under study are irradiated with a 140-$\\mathrm{GHz}$ microwave\nfield, the resistance corresponding to the main oscillation minimum, which\noccurs near the cyclotron resonance, appears to be close to zero. The results\nof the study suggest that a mobility value lower than $10^6$ $\\mathrm{cm^2/Vs}$\ndoes not prevent the formation of zero-resistance states in magnetic field in a\ntwo-dimensional system under the effect of microwave radiation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Charge frustration in a triangular triple quantum dot: We experimentally investigate the charge (isospin) frustration induced by a\ngeometrical symmetry in a triangular triple quantum dot. We observe the\nground-state charge configurations of six-fold degeneracy, the manifestation of\nthe frustration. The frustration results in omnidirectional charge transport,\nand it is accompanied by nearby nontrivial triple degenerate states in the\ncharge stability diagram. The findings agree with a capacitive interaction\nmodel. We also observe unusual transport by the frustration, which might be\nrelated to elastic cotunneling and the interference of trajectories through the\ndot. This work demonstrates a unique way of studying geometrical frustration in\na controllable way.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous Characteristics of the Generation - Recombination Noise in\n  Quasi-One-Dimensional Van der Waals Nanoribbons: We describe the low-frequency current fluctuations, i.e. electronic noise, in\nquasi-one-dimensional ZrTe3 van der Waals nanoribbons, which have recently\nattracted attention owing to their extraordinary high current carrying\ncapacity. Whereas the low-frequency noise spectral density reveals 1/f behavior\nnear room temperature, it is dominated by the Lorentzian bulges of the\ngeneration - recombination noise at low temperatures (f is the frequency).\nUnexpectedly, the corner frequency of the observed Lorentzian peaks shows\nstrong sensitivity to the applied source - drain bias. This dependence on\nelectric field can be explained by the Frenkel-Poole effect in the scenario\nwhere the voltage drop happens predominantly on the defects, which block the\nquasi-1D conduction channels. We also have found that the activation energy of\nthe characteristic frequencies of the G-R noise in quasi-1D ZrTe3 is defined\nprimarily by the temperature dependence of the capture cross-section of the\ndefects rather than by their energy position. These results are important for\nthe application of quasi-1D van der Waals materials in ultimately downscaled\nelectronics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anisotropic contribution to the van der Waals and the Casimir-Polder\n  energies for CO$_2$ and CH$_4$ molecules near surfaces and thin films: In order to understand why carbon dioxide (CO$_2$) and methane (CH$_4$)\nmolecules interact differently with surfaces, we investigate the Casimir-Polder\nenergy of a linearly polarizable CO$_2$ molecule and an isotropically\npolarizable CH$_4$ molecule in front of an atomically thin gold film and an\namorphous silica slab. We quantitatively analyze how the anisotropy in the\npolarizability of the molecule influences the van der Waals contribution to the\nbinding energy of the molecule.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Machine learning nonequilibrium electron forces for adiabatic spin\n  dynamics: We present a generalized potential theory of nonequilibrium torques for the\nLandau-Lifshitz equation. The general formulation of exchange forces in terms\nof two potential energies allows for the implementation of accurate machine\nlearning models for adiabatic spin dynamics of out-of-equilibrium itinerant\nmagnetic systems. To demonstrate our approach, we develop a deep-learning\nneural network that successfully learns the forces in a driven s-d model\ncomputed from the nonequilibrium Green's function method. We show that the\nLandau-Lifshitz dynamics simulations with forces predicted from the neural-net\nmodel accurately reproduce the voltage-driven domain-wall propagation. Our work\nopens a new avenue for multi-scale modeling of nonequilibrium dynamical\nphenomena in itinerant magnets and spintronics based on machine-learning\nmodels.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Super-fermion representation of the Lindblad master equation for the\n  electron transport problem: We discuss the use of super-fermion formalism to represent and solve quantum\nkinetic equations for the electron transport problem. Starting with the\nLindblad master equation for the molecule connected to two metal electrodes, we\nconvert the problem of finding the nonequilibrium steady state to the many-body\nproblem with non-Hermitian Liouvillian in super-Fock space. We transform the\nLiouvillian to the normal ordered form, introduce nonequilibrium quasiparticles\nby a set of canonical nonunitary transformations and develop general many-body\ntheory for the electron transport through the interacting region. The approach\nis applied to the electron transport through a single level. We consider a\nminimal basis hydrogen atom attached to two metal leads in Coulomb blockade\nregime (out of equilibrium Anderson model) within the nonequilibrium\nHartree-Fock approximation as an example of the system with electron\ninteraction. Our approach agrees with exact results given by the Landauer\ntheory for the considered models.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical conductivity as a probe of the interaction-driven metal in\n  rhombohedral trilayer graphene: Study of the strongly correlated states in van der Waals heterostructures is\none of the central topics in modern condensed matter physics. Among these, the\nrhombohedral trilayer graphene (RTG) occupies a prominent place since it hosts\na variety of interaction-driven phases, with the metallic ones yielding exotic\nsuperconducting orders upon doping. Motivated by these experimental findings,\nwe show within the framework of the low-energy Dirac theory that the optical\nconductivity can distinguish different candidates for a paramagnetic metallic\nground state in this system. In particular, this observable shows a single peak\nin the fully gapped valence-bond state. On the other hand, the bond-current\nstate features two pronounced peaks in the optical conductivity as the probing\nfrequency increases. Finally, the rotational symmetry breaking charge-density\nwave exhibits a minimal conductivity with the value independent of the\namplitude of the order parameter, which corresponds precisely to the splitting\nof the two cubic nodal points at the two valleys into two triplets of the band\ntouching points featuring linearly dispersing quasiparticles. These features\nrepresent the smoking gun signatures of different candidate order parameters\nfor the paramagnetic metallic ground state, which should motivate further\nexperimental studies of the RTG.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron-hole spin flip-flop in semiconductor quantum dots: We use temporally resolved intensity cross-correlation measurements to\nidentify the biexciton-exciton radiative cascades in a negatively charged QD.\nThe polarization sensitive correlation measurements show unambiguously that the\nexcited two electron triplet states relax non-radiatively to their singlet\nground state via a spin non conserving flip-flop with the ground state heavy\nhole. We explain this mechanism in terms of resonant coupling between the\nconfined electron states and an LO phonon. This resonant interaction together\nwith the electron-hole exchange interaction provides an efficient mechanism for\nthis, otherwise spin-blockaded, electronic relaxation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Breakdown of topological protection due to non-magnetic edge disorder in\n  two-dimensional materials in the Quantum Spin Hall phase: We study the suppression of the conductance quantization in quantum spin Hall\nsystems by a combined effect of electronic interactions and edge disorder, that\nis ubiquitous in exfoliated and CVD grown 2D materials. We show that the\ninterplay between the electronic localized states due to edge defects and\nelectron-electron interactions gives rise to local magnetic moments, that break\ntime-reversal symmetry and the topological protection of the edge states in 2D\ntopological systems. Our results suggest that edge disorder leads to small\ndeviations of a perfect quantized conductance in short samples and to a strong\nconductance suppression in long ones. Our analysis is based on on the Kane-Mele\nmodel, an unrestricted Hubbard mean field Hamiltonian and on a self-consistent\nrecursive Green's functions technique to calculate the transport quantities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological Quantum Computation Based on Chiral Majorana Fermions: Chiral Majorana fermion is a massless self-conjugate fermion which can arise\nas the edge state of certain two-dimensonal topological matters. It has been\ntheoretically predicted and experimentally observed in a hybrid device of\nquantum anomalous Hall insulator and a conventional superconductor. Its closely\nrelated cousin, Majorana zero mode in the bulk of the corresponding topological\nmatter, is known to be applicable in topological quantum computations. Here we\nshow that the propagation of chiral Majorana fermions lead to the same unitary\ntransformation as that in the braiding of Majorana zero modes, and propose a\nnew platform to perform quantum computation with chiral Majorana fermions. A\nCorbino ring junction of the hybrid device can utilize quantum coherent chiral\nMajorana fermions to implement the Hadamard gate and the phase gate, and the\njunction conductance yields a natural readout for the qubit state.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bolometric arrays and infrared sensitivity of VO2 films with varying\n  stoichiometry: Here we propose a linear microbolometric array based on VOx thin films. The\nlinear microbolometric array is fabricated by using micromachining technology,\nand its thermo-sensitive VOx thin film has excellent infrared response spectrum\nand TCR characteristics. Nano-scale VOx thin films deposited on SiO2/Si\nsubstrates were obtained by e-beam vapor deposition. The VOx films were then\nannealed at temperatures between 300 to 500 C with various deposition duration\ntime. The crystal structures and microstructures were examined by XRD, SEM and\nESCA. These films showed a predominant phase of rhombohedral VO2 and the\ncrystallinity of the VO2 increased as the annealing temperature increased.\nIntegrated with CMOS circuit, an experimentally prototypical monolithic linear\nmicrobolometric array is designed and fabricated. The testing results of the\nexperimental linear array show that the responsivity of linear array can\napproach 18KV/W and is potential for infrared image systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Generalized Bloch theorem and topological characterization: The Bloch theorem enables reduction of the eigenvalue problem of the\nsingle-particle Hamiltonian that commutes with translational group. Based on a\ngroup theory analysis we present generalization of the Bloch theorem that\nincorporates all additional symmetries of a crystal. The generalized Bloch\ntheorem constrains the form of the Hamiltonian which becomes manifestly\ninvariant under additional symmetries. In the case of isotropic interactions\nthe generalized Bloch theorem gives a unique Hamiltonian. This Hamiltonian\ncoincides with the Hamiltonian in the periodic gauge. In the case of\nanisotropic interactions the generalized Bloch theorem allows a family of\nHamiltonians. Due to the continuity argument we expect that even in this case\nthe Hamiltonian in the periodic gauge defines observables, such as Berry\ncurvature, in the inverse space. For both cases we present examples and\ndemonstrate that the average of the Berry curvatures of all possible\nHamiltonians in the Bloch gauge is the Berry curvature in the periodic gauge.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mechanisms of optical orientation of an individual Mn$^{2+}$ ion spin in\n  a II-VI quantum dot: We provide a theoretical description of the optical orientation of a single\nMn$^{2+}$ ion spin under quasi-resonant excitation demonstrated experimentally\nby Goryca et al. [Phys. Rev. Lett. 103, 087401 (2009)]. We build and analyze a\nhierarchy of models by starting with the simplest assumptions (transfer of\nperfectly spin-polarized excitons from Mn-free dot to the other dot containing\na single Mn$^{2+}$ spin, followed by radiative recombination) and subsequently\nadding more features, such as spin relaxation of electrons and holes.\nParticular attention is paid to the role of the influx of the dark excitons and\nthe process of biexciton formation, which are shown to contribute significantly\nto the orientation process in the quasi-resonant excitation case. Analyzed\nscenarios show how multiple features of the excitonic complexes in\nmagnetically-doped quantum dots, such as the values of exchange integrals, spin\nrelaxation times, etc., lead to a plethora of optical orientation processes,\ncharacterized by distinct dependencies on light polarization and laser\nintensity, and occurring on distinct timescales. Comparison with experimental\ndata shows that the correct description of the optical orientation mechanism\nrequires taking into account Mn$^{2+}$ spin-flip processes occurring not only\nwhen the exciton is already in the orbital ground state of the light-emitting\ndot, but also those that happen during the exciton transfer from high-energy\nstates to the ground state. Inspired by the experimental results on energy\nrelaxation of electrons and holes in nonmagnetic dots, we focus on the process\nof biexciton creation allowed by mutual spin-flip of an electron and the\nMn$^{2+}$ spin, and we show that by including it in the model, we obtain good\nqualitative and quantitative agreement with the experimental data on\nquasi-resonantly driven Mn$^{2+}$ spin orientation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Element-specific soft X-ray spectroscopy, scattering and imaging studies\n  of skyrmion-hosting compound Co$_8$Zn$_8$Mn$_4$: A room-temperature skyrmion-hosting compound Co$_8$Zn$_8$Mn$_4$ has been\nexamined by means of soft X-ray absorption spectroscopy, resonant small-angle\nscattering and extended reference holography. An element-selective study was\nperformed by exciting the $2p$-to-$3d$ transitions near Co and Mn $L_{2,3}$\nabsorption edges. By utilizing the coherence of soft X-ray beams the\nelement-specific real-space distribution of local magnetization at different\ntemperatures has been reconstructed using iterative phase retrieval and\nholography with extended reference. It was shown that the magnetic moments of\nCo and Mn are ferromagnetically coupled and exhibit similar magnetic patterns.\nBoth imaging methods provide a real-space resolution of 30 nm and allowed to\nrecord a magnetic texture in the temperature range between $T\\,=\\,20$ K and\n$T\\,=120\\,$ K, demonstrating the elongation of the skyrmions along the\nprincipal crystallographic axes at low temperatures. Micromagnetic simulations\nhave shown that such deformation is driven by decreasing ratio of symmetric\nexchange interaction to antisymmetric Dzyaloshinskii-Moriya interaction in the\nsystem and effect of the cubic anisotropy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Modified Confinement Model for Size Dependent Raman Shift and Linewidth\n  of Silicon Nanocrystals: A modified phonon confinement model considering the size distribution, an\nimproved phonon dispersion curve and a confinement function is developed for\nthe calculation of size dependent Raman spectra of the silicon (Si)\nnanocrystals. The model is capable in simultaneous calculation of the Raman\nshift, intensity and linewidth. The calculated size dependent redshift and\nlinewidth of Raman spectra are in good agreement with the available\nexperimental data in literature and better than previously reported theoretical\nresults. The rapid rise in the redshift and linewidth for relatively smaller Si\nnanocrystals are well reproduced. The asymmetric behavior of Raman spectra is\nalso obtained from the present model.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Antiferromagnetic Magnonic Crystals: We describe the features of magnonic crystals based upon antiferromagnetic\nelements. Our main results are that with a periodic modulation of either\nmagnetic fields or system characteristics, such as the anisotropy, it is\npossible to tailor the spin wave spectra of antiferromagnetic systems into a\nband-like organization that displays a segregation of allowed and forbidden\nbands. The main features of the band structure, such as bandwidths and\nbandgaps, can be readily manipulated. Our results provide a natural link\nbetween two steadily growing fields of spintronics: antiferromagnetic\nspintronics and magnonics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-quantized square-root topological insulators: a realization in\n  photonic Aharonov-Bohm cages: Topological Insulators are a novel state of matter where spectral bands are\ncharacterized by quantized topological invariants. This unique quantized\nnon-local property commonly manifests through exotic bulk phenomena and\ncorresponding robust boundary effects. In our work, we report a new type of\ntopological insulator exhibiting spectral bands with non-quantized topological\nproperties, but with a quantization that arises in a corresponding system where\nthe square of the Hamiltonian is taken. We provide a thorough theoretical\nanalysis as well as an experimental demonstration based on photonic\nAharonov-Bohm cages to highlight the bulk and boundary properties of this\nneophyte state of matter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Energetics and stability of vacancies in carbon nanotubes: In this work we present ab initio calculations of the formation energies and\nstability of different types of multi-vacancies in carbon nanotubes. We\ndemonstrate that, as in the case of graphene, the reconstruction of the defects\nhas drastic effects on the energetics of the tubes. In particular, the\nformation of pentagons eliminates the dangling bonds thus lowering the\nformation energy. This competition leads to vacancies having an even number of\ncarbon atoms removed to be more stable. Finally the appearance of magic numbers\nindicating more stable defects can be represented by a model for the formation\nenergies that is based on the number of dangling bonds of the unreconstructed\nsystem, the pentagons and the relaxation of the final form of the defect formed\nafter the relaxation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "On magnetic-field-induced dissipationless electric current in helicoidal\n  graphene nanoribbons: We argue that twisted (helicoidal) graphene nanoribbons may support\ndissipationless electric current in the presence of static uniform magnetic\nfield. The non-resistive charge transfer in this parity-odd system should be\nenhanced by thermal fluctuations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Giant Zeeman splitting inducing near-unity valley polarization in van\n  der Waals heterostructures: Monolayers of semiconducting transition metal dichalcogenides exhibit\nintriguing fundamental physics of strongly coupled spin and valley degrees of\nfreedom for charge carriers. While the possibility of exploiting these\nproperties for information processing stimulated concerted research activities\ntowards the concept of valleytronics , maintaining control over spin-valley\npolarization proved challenging in individual monolayers. A promising\nalternative route explores type II band alignment in artificial van der Waals\nheterostructures. The resulting formation of interlayer excitons combines the\nadvantages of long carrier lifetimes and spin-valley locking . Here, we\ndemonstrate direct magnetic manipulation of valley polarization in a WSe2/MoSe2\nheterostructure through giant valley Zeeman splitting of interlayer\ntransitions. Remarkably, even after non-selective injection, the observed $g$\nfactor as large as $-15$ induces near-unity polarization of long-lived excitons\nwith 100 ns lifetimes under magnetic fields. The demonstrated control of the\nspin-valley physics highlights the exceptional aspects of novel, artificially\ndesigned material systems and their promise for atomically-thin valleytronic\ndevices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermodynamic properties of tunneling quasiparticles in graphene-based\n  structures: Thermodynamic properties of quasiparticles in a graphene-based structures are\ninvestigated. Two graphene superconducting layers (one superconducting\ncomponent is placed on the top layeredgraphene structure and the other\ncomponent in the bottom) separated by oxide dielectric layers and one normal\ngraphene layer in the middle. The quasiparticle flow emerged due to external\ngate voltage, we considered it as a gas of electron-hole pairs whose components\nbelong to different layers. This is a striking result in view of the complexity\nof these systems: we have established that specific heat exhibits universal\n(-T3) behaviour at low T, independent from the gate voltage and the\nsuperconducting gap. The experimental observation of this theoretical\nprediction would be an important step towards our understanding of critical\nmassless matter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Resources of polarimetric sensitivity in spin noise spectroscopy: We attract attention to the fact that the ultimate (shot-noise-limited)\npolarimetric sensitivity can be enhanced by orders of magnitude leaving the\nphoton flux incident onto the photodetector on the same low level. This\nopportunity is of crucial importance for present-day spin noise spectroscopy,\nwhere a direct increase of sensitivity by increasing the probe beam power is\nstrongly restricted by the admissible input power of the broadband\nphotodetectors. The gain in sensitivity is achieved by replacing the 45-deg\npolarization geometry commonly used in conventional schemes with balanced\ndetectors by geometries with stronger polarization extinction. The efficiency\nof these high-extinction polarization geometries with enhancement of the\ndetected signal by more than an order of magnitude is demonstrated by\nmeasurements of the spin noise spectra of bulk n:GaAs in the spectral range\n835-918 nm. It is shown that the inevitable growth of the probe beam power with\nthe sensitivity gain makes spin noise spectroscopy much more perturbative, but,\nat the same time, opens up fresh opportunities for studying nonlinear\ninteractions of strong light fields with spin ensembles.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin Currents in Metallic Nanostructures; Explicit Calculations: In ultrathin ferromagnets deposited on metallic substrates, excitation of\nprecessional motion of the spins produces a spin current in the substrate that\ntransports angular momentum out of the film. This phenomenon is referred to as\nspin pumping, and is a source of damping of the spin motion. Spin pumping\nenters importantly in the description of spin dynamics in other nanoscale and\nsubnanoscale systems as well. In this paper, we present an approach based on\nthe Kubo formalism that allows the explicit calculation of this spin current\nand its spatial variation. We use the formalism to explore features of the spin\ncurrent generated by spin motions in a simple model system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Moir\u00e9 Imaging in Twisted Bilayer Graphene Aligned on Hexagonal Boron\n  Nitride: Moir\\'e superlattices (MSL) formed in angle-aligned bilayers of van der Waals\nmaterials have become a promising platform to realize novel two-dimensional\nelectronic states. Angle-aligned trilayer structures can form two sets of MSLs\nwhich could potentially interfere with each other. In this work, we directly\nimage the moir\\'e patterns in both monolayer graphene aligned on hBN and\ntwisted bilayer graphene aligned on hBN, using combined scanning microwave\nimpedance microscopy and conductive atomic force microscopy. Correlation of the\ntwo techniques reveals the contrast mechanism for the achieved ultrahigh\nspatial resolution (<2 nm). We observe two sets of MSLs with different\nperiodicities in the trilayer stack. The smaller MSL breaks the 6-fold\nrotational symmetry and exhibits abrupt discontinuities at the boundaries of\nthe larger MSL. Using a rigid atomic-stacking model, we demonstrate that the\nhBN layer considerably modifies the MSL of twisted bilayer graphene. We further\nanalyze its effect on the reciprocal space spectrum of the dual-moir\\'e system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-linear transport and heat dissipation in metallic carbon nanotubes: We show that the local temperature dependence of thermalized electron and\nphonon populations along metallic carbon nanotubes is the main reason behind\nthis non-linear transport characteristics in the high bias regime. Our model\nthat considers optical and zone boundary phonon emission as well as absorption\nby charge carriers is based on the solution of the Boltzmann transport equation\nthat assumes a local temperature along the nanotube, determined\nself-consistently with the heat transport equation. By using realistic\ntransport parameters, our results not only reproduce experimental data for\nelectronic transport, but also provide a coherent interpretation of thermal\nbreakdown under electric stress. In particular, electron and phonon\nthermalization prohibits ballistic transport in short nanotubes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Novel Exotic Magnetic Spin-order in Co5Ge3 Nano-size Materials: The Cobalt-germanium (Co-Ge) is a fascinating complex alloy system that has\nunique structure and exhibit range of interesting magnetic properties which\nwould change when reduce to nanoscale dimension. At this experimental work, the\nhigh-aspect-ratio Co5Ge3 nanoparticle with average size of 8nm was synthesized\nby gas aggregation-type cluster-deposition technology. The nanostructure\nmorphology of the as-made binary Co5Ge3 nanoparticles demonstrate excellent\nsingle-crystalline hexagonal structure with mostly preferable growth along\n(110) and (102) directions. In contrast the bulk possess Pauli paramagnetic\nspin-order at all range of temperature, here we discover size-driven new\nmagnetic ordering of as-synthesized Co5Ge3 nanoparticles exhibiting\nferromagnetism at room temperature with saturation magnetization of Ms = 32.2\nemu/cm3. This is first report of observing such new magnetic spin ordering in\nthis kind of material at nano-size which the magnetization has lower\nsensitivity to thermal energy fluctuation and exhibit high Curie temperature\nclose to 850 K. This ferromagnetic behavior along with higher Curie temperature\nat Co5Ge3 nanoparticles are attributes to low-dimension and quantum-confinement\neffect which imposes strong spin coupling and provides a new set of size-driven\nspin structures in Co5Ge3 nanoparticle which no such magnetic behavior being\npresent in the bulk of same material. This fundamental scientific study\nprovides important insights into the formation, structural, and the magnetic\nproperty of sub 10nm Co5Ge3 nanostructure which shall lead to promising\npractical versatile applications for magneto- germanide based nano-devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic transport in normal-conductor/graphene/normal-conductor\n  junctions and conditions for insulating behavior at a finite charge-carrier\n  density: We investigate the conductance of normal-conductor/graphene/normal-conductor\n(NGN) junctions for arbitrary on-site potentials in the normal and graphitic\nparts of the system. We find that a ballistic NGN junction can display\ninsulating behavior even when the charge-carrier density in the graphene part\nis finite. This effect originates in the different k intervals supporting\npropagating modes in graphene and a normal conductor, and persists for moderate\nlevels of bulk, edge, or interface disorder. The ensuing conductance thresholds\ncould be used as an electronic tool to map out details of the graphene band\nstructure in absolute k space.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A new method to epitaxially grow long-range ordered self-assembled InAs\n  quantum dots on (110) GaAs: We report on a new approach for positioning of self-assembled InAs quantum\ndots on (110) GaAs with nanometer precision. By combining self-assembly of\nquantum dots with molecular beam epitaxy on in-situ cleaved surfaces\n(cleaved-edge overgrowth) we have successfully fabricated arrays of long-range\nordered InAs quantum dots. Both atomic force microscopy and\nmicro-photoluminescence measurements demonstrate the ability to control size,\nposition, and ordering of the quantum dots. Furthermore, single dot\nphotoluminescence investigations confirm the high optical quality of the\nquantum dots fabricated.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Probing the helical edge states of a topological insulator by\n  Cooper-pair injection: We consider the proximity effect between a singlet s-wave superconductor and\nthe edge of a Quantum Spin Hall (QSH) topological insulator. We establish that\nAndreev reflection at a QSH edge state/superconductor interface is perfect\nwhile nonlocal Andreev processes through the superconductor are totally\nsuppressed. We compute the corresponding conductance and noise.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin Hall Insulator: Recent theories predict dissipationless spin current induced by an electric\nfield in doped semiconductors. Nevertheless, the charge current is still\ndissipative in these systems. In this work, we theoretically predict the\ndissipationless spin Hall effect, without any accompanying charge current, in\nsome classes of band insulators, including zero-gap semiconductors such as HgTe\nand narrow-gap semiconductors such as PbTe. This effect is similar to the\nquantum Hall effect in that all the states below the gap contribute and there\noccurs no dissipation. However the spin Hall conductance is not quantized even\nin two dimensions. This is the first example of a nontrivial topological\nstructure in a band insulator without any magnetic field.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Absence of magnetic-proximity effect at the interface of Bi$_2$Se$_3$\n  and (Bi,Sb)$_2$Te$_3$ with EuS: We performed x-ray magnetic circular dichroism (XMCD) measurements on\nheterostructures comprising topological insulators (TIs) of the\n(Bi,Sb)$_2$(Se,Te)$_3$ family and the magnetic insulator EuS. XMCD measurements\nallow us to investigate element-selective magnetic proximity effects at the\nvery TI/EuS interface. A systematic analysis reveals that there is neither\nsignificant induced magnetism within the TI nor an enhancement of the Eu\nmagnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te,\nand Se sites are lower than the estimated detection limit of the XMCD\nmeasurements of $\\sim\\!10^{-3}$ $\\mu_\\mathrm{B}$/at.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetoelectric control of topological phases in graphene: Topological antiferromagnetic (AFM) spintronics is an emerging field of\nresearch, which involves the topological electronic states coupled to the AFM\norder parameter known as the N$\\acute{\\rm e}$el vector. The control of these\nstates is envisioned through manipulation of the N$\\acute{\\rm e}$el vector by\nspin-orbit torques driven by electric currents. Here we propose a different\napproach favorable for low-power AFM spintronics, where the control of the\ntopological states in a two-dimensional material, such as graphene, is\nperformed via the proximity effect by the voltage induced switching of the\nN$\\acute{\\rm e}$el vector in an adjacent magnetoelectric AFM insulator, such as\nchromia. Mediated by the symmetry protected boundary magnetization and the\ninduced Rashba-type spin-orbit coupling at the interface between graphene and\nchromia, the emergent topological phases in graphene can be controlled by the\nN$\\acute{\\rm e}$el vector. Using density functional theory and tight-binding\nHamiltonian approaches, we model a graphene/Cr2O3 (0001) interface and\ndemonstrate non-trivial band gap openings in the graphene Dirac bands\nasymmetric between the K and K' valleys. This gives rise to an unconventional\nquantum anomalous Hall effect (QAHE) with a quantized value of $2e^2/h$ and an\nadditional step-like feature at a value close to $e^2/2h$, and the emergence of\nthe spin-polarized valley Hall effect (VHE). Furthermore, depending on the\nN$\\acute{\\rm e}$el vector orientation, we predict the appearance and\ntransformation of different topological phases in graphene across the\n$180^{\\circ}$ AFM domain wall, involving the QAHE, the valley-polarized QAHE\nand the quantum VHE (QVHE), and the emergence of the chiral edge state along\nthe domain wall. These topological properties are controlled by voltage through\nmagnetoelectric switching of the AFM insulator with no need for spin-orbit\ntorques.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Unified Semi-Classical Description of Intrinsic Spin-Hall Effect in\n  Spintronic, Optical, and Graphene Systems: A semi-classical description of the intrinsic spin-Hall effect (SHE) is\npresented which is relevant for a wide class of systems. A heuristic model for\nthe SHE is developed, starting with a fully quantum mechanical treatment, from\nwhich we construct an intuitive expression for the spin-Hall current and\nconductivity. Our method makes transparent the physical mechanism which drives\nthe effect, and unifies the SHE across several spintronic and optical systems.\nFinally, we propose an analogous effect in bilayer graphene.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Backscattering off a driven Rashba impurity at the helical edge: The spin degree of freedom is crucial for both understanding and exploiting\nthe particular properties of the edges of two-dimensional topological\ninsulators. In the absence of superconductivity and magnetism, Rashba coupling\nis the most relevant single particle perturbation in this system. Since Rashba\ncoupling does not break time reversal symmetry, its influence on transport\nproperties is only visible if processes that do not conserve the single\nparticle energy are included. Paradigmatic examples of such processes are\nelectron-electron interactions and time dependent external drivings. We analyze\nthe effects of a periodically driven Rashba impurity at the helical edge, in\nthe presence of electron-electron interactions. Interactions are treated by\nmeans of bosonization and the backscattering current is computed perturbatively\nup to second order in the impurity strength. We show that the backscattering\ncurrent is non-monotonic in the driving frequency. This property is a\nfingerprint of the Rashba impurity, being absent in the case of a magnetic\nimpurity in the helical liquid. Moreover, the non-monotonic behaviour allows us\nto directly link the backscattering current to the Luttinger parameter $K$,\nencoding the strength of electron-electron interactions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electrons imitating light: Frustrated supercritical collapse in charged\n  arrays on graphene: The photon-like electronic dispersion of graphene bestows its charge carriers\nwith unusual confinement properties that depend strongly on the geometry and\nstrength of the surrounding potential. Here we report bottom-up synthesis of\natomically-precise one-dimensional (1D) arrays of point charges aimed at\nexploring supercritical confinement of carriers in graphene for new geometries.\nThe arrays were synthesized by arranging F4TCNQ molecules into a 1D lattice on\nback-gated graphene devices, allowing precise tuning of both the molecular\ncharge state and the array periodicity. Dilute arrays of ionized F4TCNQ\nmolecules are seen to behave like isolated subcritical charges but dense arrays\nshow emergent supercriticality. In contrast to compact supercritical clusters,\nextended 1D charge arrays exhibit both supercritical and subcritical\ncharacteristics and belong to a new physical regime termed frustrated\nsupercritical collapse. Here carriers in the far-field are attracted by a\nsupercritical charge distribution, but have their fall to the center frustrated\nby subcritical potentials in the near-field, similar to the trapping of light\nby a dense cluster of stars in general relativity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Exact microscopic wave function for a topological quantum membrane: The higher dimensional quantum Hall liquid constructed recently supports\nstable topological membrane excitations. Here we introduce a microscopic\ninteracting Hamiltonian and present its exact ground state wave function. We\nshow that this microscopic ground state wave function describes a topological\nquantum membrane. We also construct variational wave functions for excited\nstates using the non-commutative algebra on the four sphere. Our approach\nintroduces a non-perturbative method to quantize topological membranes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The Synthesis and Electrical Transport of Ligand-Protected Au13 Clusters: The ligand-protected Au13 clusters have been synthesized by using\nmeso-2,3-imercaptosuccinic acid as the reducing and stabilizing agent.\nTransmission electron microscopic analysis shows a size distribution of 0.6nm.\nOptical spectrum shows an absorbance peak at 390 nm. The electrical transport\nmeasurement devices are fabricated using the electro-migration method. Coulomb\nblockade is observed at the temperature of 1.6 K,revealing the formation of the\ntunneling junction. The Coulomb oscillation on-off ratio is nearly 5. Three\npeaks are extracted in the dI-dV data and attributed to the energy levels of\nAu13 clusters, gapped by about 60 meV. First principle calculations are carried\nout to interpret the energy diagram.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Zero-Energy Modes from Coalescing Andreev States in a Two-Dimensional\n  Semiconductor-Superconductor Hybrid Platform: We investigate zero-bias conductance peaks that arise from coalescing subgap\nAndreev states, consistent with emerging Majorana zero modes, in hybrid\nsemiconductor-superconductor wires defined in a two-dimensional InAs/Al\nheterostructure using top-down lithography and gating. The measurements\nindicate a hard superconducting gap, ballistic tunneling contact, and in-plane\ncritical fields up to $3$~T. Top-down lithography allows complex geometries,\nbranched structures, and straightforward scaling to multicomponent devices\ncompared to structures made from assembled nanowires.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Programmable two-qubit gates in capacitively coupled flopping-mode spin\n  qubits: Recent achievements in the field of gate defined semiconductor quantum dots\nreinforce the concept of a spin-based quantum computer consisting of nodes of\nlocally connected qubits which communicate with each other via superconducting\ncircuit resonator photons. In this work we theoretically demonstrate a\nversatile set of quantum gates between adjacent spin qubits defined in\nsemiconductor quantum dots situated within the same node of such a spin-based\nquantum computer. The electric dipole acquired by the spin of an electron that\nmoves across a double quantum dot potential in a magnetic field gradient has\nenabled strong coupling to resonator photons and low-power spin control. Here\nwe show that this flopping-mode spin qubit also provides with the tunability to\nprogram multiple two-qubit gates. Since the capacitive coupling between these\nqubits brings about additional dephasing, we calculate the estimated infidelity\nof different two-qubit gates in the most immediate possible experimental\nrealizations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic Noise of a Single Skyrmion: To enable the practical use of skyrmion-based devices, it is essential to\nachieve a balance between energy efficiency and thermal stability, while also\nensuring reliable electrical detection against noise. Understanding how a\nskyrmion interacts with material disorder and external perturbations is thus\nessential. Here we investigate the electronic noise of a single skyrmion under\nthe influence of thermal fluctuations and spin currents in a magnetic thin\nfilm. We detect the thermally induced noise with a 1/f signature in the strong\npinning regime but a random telegraph noise in the intermediate pinning regime.\nBoth the thermally dominated and current-induced telegraph-like signals are\ndetected in the weak pinning regime. Our results provide a comprehensive\nelectronic noise picture of a single skyrmion, demonstrating the potential of\nnoise fluctuation as a valuable tool for characterizing the pinning condition\nof a skyrmion. These insights could also aid in the development of low-noise\nand reliable skyrmion-based devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Charging effects in the inductively shunted Josephson junction: The choice of impedance used to shunt a Josephson junction determines if the\ncharge transferred through the circuit is quantized: a capacitive shunt renders\nthe charge discrete, whereas an inductive shunt leads to continuous charge.\nThis discrepancy leads to a paradox in the limit of large inductances L. We\nshow that while the energy spectra of the capacitively and inductively shunted\njunction are vastly different, their high-frequency responses become identical\nfor large L. Inductive shunting thus opens the possibility to observe charging\neffects unimpeded by charge noise.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Enhanced thermoelectric properties in hybrid graphene-boron nitride\n  nanoribbons: The thermoelectric properties of hybrid graphene-boron nitride nanoribbons\n(BCNNRs) are investigated using the non-equilibrium Green's function (NEGF)\napproach. We find that the thermoelectric figure of merit (ZT) can be\nremarkably enhanced by periodically embedding hexagonal BN (h-BN) into graphene\nnanoribbons (GNRs). Compared to pristine GNRs, the ZT for armchair-edged BCNNRs\nwith width index 3p+2 is enhanced up to 10~20 times while the ZT of nanoribbons\nwith other widths is enhanced just by 1.5~3 times. As for zigzag-edge\nnanoribbons, the ZT is enhanced up to 2~3 times. This improvement comes from\nthe combined increase in the Seebeck coefficient and the reduction in the\nthermal conductivity outweighing the decrease in the electrical conductance. In\naddition, the effect of component ratio of h-BN on the thermoelectric transport\nproperties is discussed. These results qualify BCNNRs as a promising candidate\nfor building outstanding thermoelectric devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Light Induced Aggregation of Specific Single Walled Carbon Nanotubes: We report optically induced aggregation and consequent separation of specific\ndiameter of pristine single walled carbon nanotubes (SWNT) from stable\nsolution. Well dispersed solution of pristine SWNTs, without any surfactant or\nfunctionalization, show rapid aggregation by uniform exposure to UV, visible\nand NIR illumination. Optically induced aggregation linearly increases with\nconsequent increase in the intensity of light. Aggregated SWNTs were separated\nfrom the dispersed supernatant and characterized using absorption and Raman\nspectroscopy. Separated SWNTs distinctly show enrichment of specific SWNTs\nunder UV visible and NIR illumination.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dissipation-driven quantum phase transitions in a Tomonaga-Luttinger\n  liquid electrostatically coupled to a metallic gate: The dissipation induced by a metallic gate on the low-energy properties of\ninteracting 1D electron liquids is studied. As function of the distance to the\ngate, or the electron density in the wire, the system undergoes a quantum phase\ntransition from the Tomonaga-Luttinger liquid state to two kinds of dissipative\nphases, one of them with a finite spatial correlation length. We also define a\ndual model, which describes an attractive one dimensional metal with a\nJosephson coupling to a dirty metallic lead.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Raman Photogalvanic Effect: photocurrent at inelastic light scattering: We show theoretically that electromagnetic waves propagating in the\ntransparency region of a non-centrosymmetric medium can induce a dc electric\ncurrent. The origin of the effect is the Raman scattering of light by free\ncarriers in the system. Due to the photon scattering, electrons undergo real\nquantum transitions resulting in the formation of their anisotropic momentum\ndistribution and in shifts of electronic wavepackets giving rise to a steady\nstate photocurrent. We present microscopic theory of the Raman Photogalvanic\neffect (RPGE) focusing on two specific situations: (i) generic case of a bulk\ngyrotropic semiconductor and (ii) a quantum well structure where the light is\nscattered by intersubband excitations. We uncover the relation of the predicted\nRPGE and the traditional photogalvanic effect at the light absorption.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Study of intrinsic spin and orbital Hall effects in Pt based on a (6s,\n  6p, 5d) tight-binding model: We study the origin of the intrinsic spin Hall conductivity (SHC) and the\nd-orbital Hall conductivity (OHC) in Pt based on a multiorbital tight-binding\nmodel with spin-orbit interaction. We find that the SHC reaches 1000\n\\hbar/e\\Omega cm when the resistivity \\rho is smaller than ~10 \\mu\\Omega cm,\nwhereas it decreases to 300 \\hbar/e\\Omega cm when \\rho ~ 100 \\mu\\Omega cm. In\naddition, the OHC is still larger than the SHC. The origin of huge SHE and OHE\nin Pt is the large ``effective magnetic flux'' that is induced by the\ninterorbital transition between d_{xy}- and d_{x2-y2}-orbitals with the aid of\nthe strong spin-orbit interaction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ultrafast mapping of optical polarization states onto spin coherence of\n  localized electrons in a semiconductor: We experimentally demonstrate an ultrafast method for preparing spin states\nof donor-bound electrons in GaAs with single laser pulses. Each polarization\nstate of a preparation pulse has a direct mapping onto a spin state, with\nbijective correspondence between the Poincar\\'{e}-sphere (for photon\npolarization) and Bloch-sphere (for spin) state representations. The\npreparation is governed by a stimulated Raman process and occurs orders of\nmagnitude faster than the spontaneous emission and spin dephasing. Similar\ndynamics governs our ultrafast optical Kerr detection of the spin coherence,\nthus getting access to spin state tomography. Experiments with double\npreparation pulses show an additive character for the preparation method.\nUtilization of these phenomena is of value for quantum information schemes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Modeling ultrafast all-optical switching in synthetic ferrimagnets: Based on numerical simulations, we demonstrate thermally induced magnetic\nswitching in synthetic ferrimagnets composed of multilayers of rare-earth and\ntransition metals. Our findings show that deterministic magnetization reversal\noccurs above a certain threshold temperature if the ratio of transition metal\natoms to rare-earth atoms is sufficiently large. Surprisingly, the total\nthickness of the multilayer system has little effect on the occurence of\nswitching. We further provide a simple argument to explain the temperature\ndependence of the reversal process.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Size Dependence of the Multiple Exciton Generation Rate in CdSe Quantum\n  Dots: The multiplication rates of hot carriers in CdSe quantum dots are quantified\nusing an atomistic pseudopotential approach and first order perturbation\ntheory. Both excited holes and electrons are considered, and electron-hole\nCoulomb interactions are accounted for. We find that holes have much higher\nmultiplication rates than electrons with the same excess energy due to the\nlarger density of final states (positive trions). When electron-hole pairs are\ngenerated by photon absorption, however, the net carrier multiplication rate is\ndominated by photogenerated electrons, because they have on average much higher\nexcess energy. We also find, contrary to earlier studies, that the effective\nCoulomb coupling governing carrier multiplication is energy dependent. We show\nthat smaller dots result in a decrease in the carrier multiplication rate for a\ngiven absolute photon energy. However, if the photon energy is scaled by the\nvolume dependent optical gap, then smaller dots exhibit an enhancement in\ncarrier multiplication for a given relative energy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Rectification and nonlinear transport in chaotic dots and rings: We investigate the nonlinear current-voltage characteristic of mesoscopic\nconductors and the current generated through rectification of an alternating\nexternal bias. To leading order in applied voltages both the nonlinear and the\nrectified current are quadratic. This current response can be described in\nterms of second order conductance coefficients and for a generic mesoscopic\nconductor they fluctuate randomly from sample to sample. Due to Coulomb\ninteractions the symmetry of transport under magnetic field inversion is broken\nin a two-terminal setup. Therefore, we consider both the symmetric and\nantisymmetric nonlinear conductances separately. We treat interactions\nself-consistently taking into account nearby gates.\n  The nonlinear current is determined by different combinations of second order\nconductances depending on the way external voltages are varied away from an\nequilibrium reference point (bias mode). We discuss the role of the bias mode\nand circuit asymmetry in recent experiments. In a photovoltaic experiment the\nalternating perturbations are rectified, and the fluctuations of the nonlinear\nconductance are shown to decrease with frequency. Their asymptotical behavior\nstrongly depends on the bias mode and in general the antisymmetric conductance\nis suppressed stronger then the symmetric conductance.\n  We next investigate nonlinear transport and rectification in chaotic rings.\nTo this extent we develop a model which combines a chaotic quantum dot and a\nballistic arm to enclose an Aharonov-Bohm flux. In the linear two-probe\nconductance the phase of the Aharonov-Bohm oscillation is pinned while in\nnonlinear transport phase rigidity is lost. We discuss the shape of the\nmesoscopic distribution of the phase and determine the phase fluctuations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Controlling surface charge and spin density oscillations by Dirac\n  plasmon interaction in thin topological insulators: We study the selective excitation at infrared and THz frequencies of optical\nand acoustic plasmonic modes supported by thin topological insulators. These\nmodes are characterized by effective net charge or net spin density,\nrespectively, and we study their excitation by combining many-body and\nelectromagnetic calculations. We first show that non-locality can significantly\nmodify the plasmonic response: it changes the energy of propagating plasmons up\nto tens of percent. We then discuss how, by changing the distance between a\ndipolar source and a semi-infinite 10 nm thin film, it is possible to control\nthe excitation of acoustic and optical propagating plasmons, which can\npropagate over a distance of several plasmonic wavelengths. Furthermore, we\nconsider 10 nm thin TI nanodisks and study the excitation of acoustic and\noptical localized plasmon modes by a point dipole source and plane wave\nillumination, respectively. The resonant plasmonic modes appear at frequencies\nthat strongly depends on the size of the disk, and that can be potentially\ntuned by applying electrostatic gating to modify the Fermi Energy of the\nconductive 2-dimensional layer that forms at the interfaces of the TI. We\nobserve a spectral shift from ~29 $\\mu$m to ~34 $\\mu$m by changing the Fermi\nEnergy from 250meV to 350meV. Last, the electromagnetic energy of these\nplasmonics modes can be confined to very small regions, of effective volume\n~(120 nm)^3 for the smaller disk considered, much less than the free-space\nwavelength cubed $\\lambda$^3 ~(35000 nm)^3. The strong confinement is desirable\nfor achieving very efficient coupling with nearby systems. Our detailed study\nthus shows that thin topological insulators are a promising system to control\nboth the spin and charge oscillations associated with the plasmonic resonances,\nwith possible applications to fast, compact and electrically-controlled\nspintronics devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-flip transitions between Zeeman sublevels in semiconductor quantum\n  dots: We have studied spin-flip transitions between Zeeman sublevels in GaAs\nelectron quantum dots. Several different mechanisms which originate from\nspin-orbit coupling are shown to be responsible for such processes.\n  It is shown that spin-lattice relaxation for the electron localized in a\nquantum dot is much less effective than for the free electron. The spin-flip\nrates due to several other mechanisms not related to the spin-orbit interaction\nare also estimated.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Disentangling electron- and electric field-induced ring-closing\n  reactions in a diarylethene derivative on Ag(111): Using scanning tunneling microscopy and spectroscopy we investigate the\nadsorption properties and ring-closing reaction of a diarylethene derivative\n(C5F-4Py) on a Ag(111) surface. We identify an electron-induced reaction\nmechanism, with a quantum yield varying from $10^{-14}-10^{-9}$ per electron\nupon variation of the bias voltage from $1-2$ V. We ascribe the drastic\nincrease in switching efficiency to a resonant enhancement upon tunneling\nthrough molecular orbitals. Additionally, we resolve the ring-closing reaction\neven in the absence of a current passing through the molecule. In this case the\nelectric-field can modify the reaction barrier, leading to a finite switching\nprobability at 4.8 K. A detailed analysis of the switching events shows that a\nsimple plate-capacitor model for the tip-surface junction is insufficient to\nexplain the distance dependence of the switching voltage. Instead, describing\nthe tip as a sphere is in agreement with the findings. We resolve small\ndifferences in the adsorption configuration of the closed isomer, when\ncomparing the electron- and field-induced switching product.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Index theorems, generalized Hall currents and topology for gapless\n  defect fermions: We show how the index of the fermion operator from the Euclidean action can\nbe used to uncover the existence of gapless modes living on defects (such as\nedges and vortices) in topological insulators and superconductors. The 1-loop\nFeynman diagram that computes the index reveals an analog of the Quantum Hall\ncurrent flowing on and off the defect -- even in systems without conserved\ncurrents or chiral anomalies -- and makes explicit the interplay between\ntopology in momentum and coordinate space. We provide several explicit\nexamples.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunneling Conductance in a Two-dimensional Dirac Semimetal Protected by\n  Non-symmorphic Symmetry: We theoretically study a tunneling effect in a two-dimensional Dirac\nsemimetal with two Dirac points protected by non-symmorphic symmetries. The\ntunnel barrier can be arranged by a magnetic exchange potential which opens a\ngap at the Dirac points which can be induced by a magnetic proximity effect of\na ferromagnetic insulator. We found that the tunnel decay length increases with\na decrease in the strength of the spin-orbit coupling, and moreover the\ndependence is attributed to the correlation of sublattice and spin degree of\nfreedoms which lead to symmetry-protected Dirac points. The tunnel probability\nis quite different in two Dirac points, and thus the tunnel effect can be\napplied to the highly-selective valley filter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spontaneous interlayer exciton coherence in quantum Hall bilayers at\n  nu=1 and nu=2: a tutorial: This tutorial paper reviews some of the physics of quantum Hall bilayers with\na focus on the case where there is low or zero tunnelling between the two\nlayers. We describe the interlayer coherent states at filling factors nu=1 and\nnu=2 as exciton condensates and discuss some of the theory associated with\nthese states.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effective medium theory for disordered two-dimensional graphene: We develop an Effective Medium Theory to study the electrical transport\nproperties of disordered graphene. The theory includes non-linear screening and\nexchange-correlation effects allowing us to consider experimentally relevant\nstrengths of the Coulomb interaction. Assuming random Coulomb impurities, we\ncalculate the electrical conductivity as a function of gate voltage describing\nquantitatively the full cross-over from the fluctuations dominated regime\naround the Dirac point to the large doping regime at high gate voltages. We\nfind that the conductivity at the Dirac point is strongly affected by exchange\ncorrelation effects.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Layered Opposite Rashba Spin-Orbit Coupling in Bilayer Graphene: Loss of\n  Spin Chirality, Symmetry Breaking and Topological Transition: Inversion symmetry in bilayer graphene allows for layered opposite Rashba\nspin-orbit coupling (LO-RSOC) -- the situation when the RSOC has the same\nmagnitude but the opposite sign in two coupled spatially separated layers. We\nshow that the LO-RSOC results in the loss of spin chirality in the momentum\nspace, in contrast to the common uniform RSOC. This chirality loss makes it\ndifficult to experimentally establish whether the LO-RSOC (on the scale of 10\nmeV) exists, because the band structure is insensitive to it. To solve this\nproblem, we propose to identify the LO-RSOC either by gating to break the\ninversion symmetry or by magnetic field to break the time-reversal symmetry.\nRemarkably, we observe the transition between trivial and non-trivial band\ntopology as the system deviates from the LO Rashba state. Ab inito calculations\nsuggest that bilayer graphene encapsulated by two monolayers of Au is a\ncandidate to be a LO Rashba system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Prediction of the Magnetotoroidic Effect from Atomistic Simulations: An effective Hamiltonian technique is used to investigate the effect of\napplying curled electric fields on physical properties of stress-free BiFeO3\ndots being under open-circuit electrical boundary conditions. It is discovered\nthat such fields can lead to a control of not only the magnitude but also the\ndirection of the magnetization. On a microscopic point of view, such control\noriginates from the field-induced transformation or switching of electrical\nvortices and their couplings with oxygen octahedral tilts and magnetic dipoles.\nThis control involves striking intermediate states, and constitutes a novel\nphenomenon that can be termed as \"magnetotoroidic\" effect.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Partition Functions of Non-Abelian Quantum Hall States: Partition functions of edge excitations are obtained for non-Abelian Hall\nstates in the second Landau level, such as the anti-Read-Rezayi state, the\nBonderson-Slingerland hierarchy and the Wen non-Abelian fluid, as well as for\nthe non-Abelian spin-singlet state. The derivation is straightforward and\nunique starting from the non-Abelian conformal field theory data and solving\nthe modular invariance conditions. The partition functions provide a complete\naccount of the excitation spectrum and are used to describe experiments of\nCoulomb blockade and thermopower.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A fast, sensitive, room-temperature graphene nanomechanical bolometer: Bolometers are a powerful and vital means of detecting light in the IR to THz\nfrequencies, and they have been adopted for a range of uses from astronomical\nobservation to thermal imaging. As uses diversify, there is an increasing\ndemand for faster, more sensitive room-temperature bolometers. To this end,\ngraphene has generated interest because of its miniscule heat capacity and its\nintrinsic ultra-broadband absorption, properties that would allow it to quickly\ndetect low levels of light of nearly any wavelength. Yet, graphene has\ndisappointed its expectations in traditional electrical bolometry at room\ntemperature, because of its weakly temperature-dependent resistivity and\nexceptionally high thermal conductivity. Here, we overcome these challenges\nwith a new approach that detects light by tracking the resonance frequency of a\ngraphene nanomechanical resonator. The absorbed light heats up and thermally\ntensions the resonator, thereby changing its frequency. Using this approach, we\nachieve a room-temperature noise-equivalent power of 7 pW/Hz^1/2, a value 100\ntimes more sensitive than electrical graphene bolometers, and speeds (1.3 MHz)\nthat greatly surpass state-of-the-art microbolometers.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetization damping in a local-density approximation: The linear response of itinerant transition metal ferromagnets to transverse\nmagnetic fields is studied in a self-consistent adiabatic local-density\napproximation. The susceptibility is calculated from a microscopic Hamiltonian,\nincluding spin-conserving impurities, impurity induced spin-orbit interaction\nand magnetic impurities using the Keldysh formalism. The Gilbert damping\nconstant in the Landau-Lifshitz-Gilbert equation is identified, parametrized by\nan effective transverse spin dephasing rate, and is found to be inversely\nproportional to the exchange splitting. Our result justify the phenomenological\ntreatment of transverse spin dephasing in the study of current-induced\nmagnetization dynamics in weak, itinerant ferromagnets by Tserkovnyak\n\\textit{et al.}. We show that neglect of gradient corrections in the\nquasiclassical transport equations leads to incorrect results when the exchange\npotential becomes of the order of the Fermi energy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interaction of phonons with discrete breather in strained graphene: We numerically analyze the interaction of small-amplitude phonon waves with\nstanding gap discrete breather (DB) in strained graphene. To make the system\nsupport gap DB, strain is applied to create a gap in the phonon spectrum. We\nonly focus on the in-plane phonons and DB, so the issue is investigated under a\nquasi-one-dimensional setup. It is found that, for the longitudinal sound waves\nhaving frequencies below 6 THz, DB is transparent and thus no radiation of\nenergy from DB takes place; whereas for those sound waves with higher\nfrequencies within the acoustic (optical) phonon band, phonon is mainly\ntransmitted (reflected) by DB, and concomitantly, DB radiates its energy when\ninteracting with phonons. The latter case is supported by the fact that, the\nsum of the transmitted and reflected phonon energy densities is noticeably\nhigher than that of the incident wave. Our results here may provide insight\ninto energy transport in graphene when the spatially localized nonlinear\nvibration modes are presented.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic transport in Si nanowires: Role of bulk and surface disorder: We calculate the resistance and mean free path in long metallic and\nsemiconducting silicon nanowires (SiNWs) using two different numerical\napproaches: A real space Kubo method and a recursive Green's function method.\nWe compare the two approaches and find that they are complementary: depending\non the situation a preferable method can be identified. Several numerical\nresults are presented to illustrate the relative merits of the two methods. Our\ncalculations of relaxed atomic structures and their conductance properties are\nbased on density functional theory without introducing adjustable parameters.\nTwo specific models of disorder are considered: Un-passivated, surface\nreconstructed SiNWs are perturbed by random on-site (Anderson) disorder whereas\ndefects in hydrogen passivated wires are introduced by randomly removed H\natoms. The un-passivated wires are very sensitive to disorder in the surface\nwhereas bulk disorder has almost no influence. For the passivated wires, the\nscattering by the hydrogen vacancies is strongly energy dependent and for\nrelatively long SiNWs (L>200 nm) the resistance changes from the Ohmic to the\nlocalization regime within a 0.1 eV shift of the Fermi energy. This high\nsensitivity might be used for sensor applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological electronic states and thermoelectric transport at phase\n  boundaries in single-layer WSe$_2$: An effective Hamiltonian theory: Monolayer transition metal dichalcogenides in the distorted octahedral\n1T$^\\prime$ phase exhibit a large bulk bandgap and gapless boundary states,\nwhich is an asset in the ongoing quest for topological electronics. In\nsingle-layer tungsten diselenide (WSe$_2$), the boundary states have been\nobserved at well ordered interfaces between 1T$^\\prime$ and semiconducting (1H)\nphases. This paper proposes an effective 4-band theory for the boundary states\nin single-layer WSe$_2$,describing a Kramers pair of in-gap states as well as\nthe behaviour at the spectrum termination points on the conduction and valence\nbands of the 1T$^\\prime$ phase. The spectrum termination points determine the\ntemperature and chemical potential dependences of the ballistic conductance and\nthermopower at the phase boundary. Notably, the thermopower shows an ambipolar\nbehaviour, changing the sign in the bandgap of the 1T$^\\prime$ - WSe$_2$ and\nreflecting its particle-hole asymmetry. The theory establishes a link between\nthe bulk band structure and ballistic boundary transport in single-layer\nWSe$_2$ and is applicable to a range of related topological materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-wave diode and circulator based on unidirectional coupling: In magnonics, an emerging branch of wave physics characterized by low-energy\nconsumption, it is highly desirable to realize circuit elements within the\nscope of spin-wave computing. Here, based on numerical simulations, we\ndemonstrate the functionality of the spin-wave diode and the circulator to\nsteer and manipulate spin waves over a wide range of frequency in the GHz\nregime. They take advantage of the unidirectional coupling induced by the\ninterfacial Dzyaloshinskii-Moriya interaction to transfer the spin wave between\nthin ferromagnetic layers in only one direction of propagation. Using the\nmultilayered structure consisting of Py and Co in direct contact with Pt, we\nobtain sub-micrometer-size devices of high efficiency. In the diode, the power\nloss ratio between forward and reverse direction reaches 22 dB, while in the\nfour-port circulator, the efficiency exceeds 13 dB. Thus, our work contributes\nto the emerging branch of energy-efficient magnonic logic devices, where,\nthanks to short wavelength of spin waves, it is possible to realize nanoscale\ndevices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Two-dimensional group delay in graphene probed by spin precession\n  measurements: We take graphene as an example to demonstrate that the present widely adopted\nexpression is only the scattering component of a true 2D group delay in the\ncondensed matter context, in which the spatial Goos-H\\\"{a}nchen (GH) shift\nalong an interface contributes an intrinsic component. We relate the dwell time\nto spin precession and derive a relation between the 2D group delay and dwell\ntime, whereby we for the first time reveal that, the group delay for 2D\nballistic electronic systems can be directly observed by measuring a\nconductance difference in a weak-field spin precession experiment. This\nphysical observable not only implies the group delay being a relevant quantity\neven in the condensed matter context, but also provides an experimental\nevidence for the intrinsic effect of the GH shift. Finally, we revisit the 2D\nHartman effect, a central issue of the group delay, by analytically solving it\nvia the vested relation and calculating the proposed observable at the Dirac\npoint.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Unconventional transport properties in systems with triply degenerate\n  quadratic band crossings: A quadratic band crossing (QBC) is a crossing of two bands with quadratic\ndispersion, which has been intensively investigated due to its appearance in\nBernal-stacked bilayer graphene. Here, we study an extension of QBCs, the\ntriply degenerate quadratic band crossing (TQBC), which is a three-band\ncrossing node containing two quadratic dispersing bands and a flat band. We\nfocus on two types of TQBCs. The first type contains a symmetry-protected QBC\nand a free-electron band, the prototype of which is the AA-stacked bilayer\nsquareoctagon lattice. In a magnetic field, such a TQBC exhibits an anomalous\nLandau level structure, leading to a distinctive quantum Hall effect which\ndisplays an infinite ladder of Hall plateaus when the chemical potential\napproaches zero. The other type of TQBC can be viewed as a pseudospin-1\nextension of the bilayer-graphene QBC. Under perturbations, this type of TQBCs\nmay split into linear pseudospin-1 Dirac-Weyl fermions. When tunneling through\na potential barrier, the transmission probability of the first type decays\nexponentially with the barrier width for any incident angle, similar to the\nfree-electron case, while the second type hosts an all-angle perfect reflection\nwhen the energy of the incident particles is equal to half the barrier height.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Intervalley scattering of graphene massless Dirac fermions at 3-periodic\n  grain boundaries: We study how low-energy charge carriers scatter off periodic and linear\ngraphene grain boundaries oriented along the zigzag direction with a\nperiodicity three times greater than that of pristine graphene. These defects\nmap the two Dirac points into the same position, and thus allow for intervalley\nscattering to occur. Starting from graphene's first-neighbor tight-binding\nmodel we show how can we compute the boundary condition seen by graphene's\nmassless Dirac fermions at such grain boundaries. We illustrate this procedure\nfor the 3-periodic pentagon-only grain boundary, and then work out the\nlow-energy electronic scattering off this linear defect. We also compute the\neffective generalized potential seen by the Dirac fermions at the grain\nboundary region.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Resistance of a Molecule: In recent years, several experimental groups have reported measurements of\nthe current-voltage (I-V) characteristics of individual or small numbers of\nmolecules. Our purpose in this chapter is to provide an intuitive explanation\nfor the observed I-V characteristics using simple models to illustrate the\nbasic physics. In contrast to the MOSFET, whose I-V is largely dominated by\nclassical electrostatics, the I-V characteristics of molecules is determined by\na more interesting interplay between nineteenth century physics\n(electrostatics) and twentieth century physics (quantum transport) and it is\nimportant to do justice to both aspects.\n  We start with a qualitative discussion of the main factors affecting the I-V\ncharacteristics of molecular conductors, using a simple toy model to illustrate\ntheir role. Including the effects of: (1) Shift in the energy level due to\ncharging effects and (2) broadening of the energy levels due to the coupling to\nthe two contacts we obtain realistic I-V plots, even though the toy model\nassumes that conduction takes place independently through individual molecular\nlevels. In general, however, the full non-equilibrium Green's function (NEGF)\nformalism is needed. Here, we describe the NEGF formalism as a generalized\nversion of the one-level model. This formalism provides a convenient framework\nfor describing quantum transport and can be used in conjunction with ab initio\nor semi-empirical Hamiltonians. A simple semi-empirical model for a gold wire\nserves to illustrate the full NEGF formalism. This example is particularly\ninstructive because it shows the lowest possible \"Resistance of a 'Molecule'\"\nper channel.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Noise-created bistability and stochastic resonance of impurities\n  diffusing in a semiconductor layer: We investigate the dynamics of impurities walking along a semiconductor layer\nassisted by thermal noise of strength $D$ and external harmonic potential\n$V(x)$. Applying a nonhomogeneous hot temperature in the vicinity of the\npotential minimum may modify the external potential into a bistable effective\npotential.\n  We propose the ways of mobilizing and eradicating the unwanted impurities\nalong the semiconductor layer. Furthermore, the thermally activated rate of\nhopping for the impurities as a function of the model parameters is studied in\nhigh barrier limit. Via two state approximation, we also study the stochastic\nresonance (SR) of the impurities dynamics where the same noise source that\ninduces the dynamics also induces the transition from mono-stable to bistable\nstate which leads to SR in the presence of time varying field.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Valley-Spin Polarization in the Magneto-Optical Response of Silicene and\n  Other Similar 2D Crystals: We calculate the magneto-optical conductivity and electronic density of\nstates for silicene, the silicon equivalent of graphene, and similar crystals\nsuch as germanene. In the presence of a perpendicular magnetic field and\nelectric field gating, we note that four spin- and valley-polarized levels can\nbe seen in the density of states and transitions between these levels lead to\nsimilarly polarized absorption lines in the longitudinal, transverse Hall, and\ncircularly polarized dynamic conductivity. While previous spin and\nvalley-polarization predicted for the conductivity is only present in the\nresponse to circularly polarized light, we show that distinct spin- and\nvalley-polarization can also be seen in the longitudinal magneto-optical\nconductivity at experimentally attainable energies. The frequency of the\nabsorption lines may be tuned by the electric and magnetic field to onset in a\nrange varying from THz to the infrared. This potential to isolate charge\ncarriers of definite spin and valley label may make silicene a promising\ncandidate for spin- and valleytronic devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Metal-insulator transition and tunable Dirac-cone surface state in the\n  topological insulator TlBi1-xSbxTe2 studied by angle-resolved photoemission: We report a systematic angle-resolved photoemission spectroscopy on\ntopological insulator (TI) TlBi1-xSbxTe2 which is bulk insulating at 0.5 < x <\n0.9 and undergoes a metal-insulator-metal transition with the Sb content x. We\nfound that this transition is characterized by a systematic hole doping with\nincreasing x, which results in the Fermi-level crossings of the bulk conduction\nand valence bands at x~ 0 and x~1, respectively. The Dirac point of the\ntopological surface state is gradually isolated from the valence-band edge,\naccompanied by a sign reversal of Dirac carriers. We also found that the Dirac\nvelocity is the largest among known solid-solution TI systems. The\nTlBi1-xSbxTe2 system thus provides an excellent platform for Dirac-cone\nengineering and device applications of TIs.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Canted ground state in artificial molecules at high magnetic fields: We analyze the transitions that a magnetic field provokes in the ground state\nof an artificial homonuclear diatomic molecule. For that purpose, we have\nperformed numerical diagonalizations for a double quantum dot around the regime\nof filling factor 2. We present phase diagrams in terms of tunneling and Zeeman\ncouplings, and confinement strength. We identify a series of transitions from\nferromagnetic to symmetric states through a set of canted states with\nantiferromagnetic couping between the two quantum dots.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Renormalization of the dephasing by zero point fluctuations: We study the role of zero-point-fluctuations (ZPF) in dephasing at low\ntemperature. Unlike the Caldeira-Leggett model where the interaction is with an\nhomogeneous fluctuating field of force, here we consider the effect of short\nrange scattering by localized bath modes. We find that in presence of ZPF the\ninelastic cross-section gets renormalized. Thus indirectly ZPF might contribute\nto the dephasing at low temperature.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current-induced skyrmion motion on magnetic nanotubes: Magnetic skyrmions are believed to be the promising candidate of information\ncarriers in spintronics. However, the skyrmion Hall effect due to the\nnontrivial topology of skyrmions can induce a skyrmion accumulation or even\nannihilation at the edge of the devices, which hinders the real-world\napplications of skyrmions. In this work, we theoretically investigate the\ncurrent-driven skyrmion motion on magnetic nanotubes which can be regarded as\n\"edgeless\" in the tangential direction. By performing micromagnetic\nsimulations, we find that the skyrmion motion exhibits a helical trajectory on\nthe nanotube, with its axial propagation velocity proportional to the current\ndensity. Interestingly, the skyrmion's annular speed increases with the\nincrease of the thickness of the nanotube. A simple explanation is presented.\nSince the tube is edgeless for the tangential skyrmion motion, a stable\nskyrmion propagation can survive in the presence of a very large current\ndensity without any annihilation or accumulation. Our results provide a new\nroute to overcome the edge effect in planar geometries.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magneto-intersubband resistance oscillations in GaAs quantum wells\n  placed in a tilted magnetic field: The magnetotransport of highly mobile 2D electrons in wide GaAs single\nquantum wells with three populated subbands placed in titled magnetic fields is\nstudied. The bottoms of the lower two subbands have nearly the same energy\nwhile the bottom of the third subband has a much higher energy ($E_1\\approx\nE_2<<E_3$). At zero in-plane magnetic fields magneto-intersubband oscillations\n(MISO) between the $i^{th}$ and $j^{th}$ subbands are observed and obey the\nrelation $\\Delta_{ij}=E_j-E_i=k\\cdot\\hbar\\omega_c$, where $\\omega_c$ is the\ncyclotron frequency and $k$ is an integer. An application of in-plane magnetic\nfield produces dramatic changes in MISO and the corresponding electron\nspectrum. Three regimes are identified. At $\\hbar\\omega_c \\ll \\Delta_{12}$ the\nin-plane magnetic field increases considerably the gap $\\Delta_{12}$, which is\nconsistent with the semi-classical regime of electron propagation. In contrast\nat strong magnetic fields $\\hbar\\omega_c \\gg \\Delta_{12}$ relatively weak\noscillating variations of the electron spectrum with the in-plane magnetic\nfield are observed. At $\\hbar\\omega_c \\approx \\Delta_{12}$ the electron\nspectrum undergoes a transition between these two regimes through magnetic\nbreakdown. In this transition regime MISO with odd quantum number $k$\nterminate, while MISO corresponding to even $k$ evolve $continuously$ into the\nhigh field regime corresponding to $\\hbar\\omega_c \\gg \\Delta_{12}$",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quasiparticle Interference Studies of Quantum Materials: Exotic electronic states are realized in novel quantum materials. This field\nis revolutionized by the topological classification of materials. Such\ncompounds necessarily host unique states on their boundaries. Scanning\ntunneling microscopy studies of these surface states have provided a wealth of\nspectroscopic characterization, with the successful cooperation of ab initio\ncalculations. The method of quasiparticle interference imaging proves to be\nparticularly useful for probing the dispersion relation of the surface bands.\nHerein, how a variety of additional fundamental electronic properties can be\nprobed via this method is reviewed. It is demonstrated how quasiparticle\ninterference measurements entail mesoscopic size quantization and the\nelectronic phase coherence in semiconducting nanowires; helical spin protection\nand energy-momentum fluctuations in a topological insulator; and the structure\nof the Bloch wave function and the relative insusceptibility of topological\nelectronic states to surface potential in a topological Weyl semimetal.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Graphene Terahertz Absorption: The unique terahertz properties of graphene has been identified for novel\noptoelectronic applications. In a graphene sample with bias voltage added,\nthere is an enhanced absorption in the far infrared region and a diminished\nabsorption in the infrared region. The strength of enhancement(diminishment)\nincreases with the gate voltage, and the enhancement compensates the\ndiminishment. We find that it is the coherence length of electrons in graphene\nthat allows pure electronic transitions between states differing by small\nmomentums and makes intraband transition possible, is responsible for the far\ninfrared enhancement. Phonon assisted processes are not necessary and would not\nin any case contribute to a sum rule. This naturally leads to results obeying\nthe general sum-rule in optical absorptions. Our prediction of the strength of\nenhancement(diminishment) in terms of the bias agrees with experiments. This is\nthe first direct calculation we are aware of, since the prior phonon assisted\nmodel for indirect transition should not obey a sum rule.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Suppression of the Persistent Spin Hall Current by Defect Scattering: We study the linear response spin Hall conductivity of a two-dimensional\nelectron gas (2DEG) in the presence of the Rashba spin orbit interaction in the\ndiffusive transport regime. When defect scattering is modeled by isotropic\nshort-range potential scatterers the spin Hall conductivity vanishes due to the\nvertex correction. A non-vanishing spin Hall effect may be recovered for\ndominantly forward defect scattering.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological phases of quantized light: Topological photonics is an emerging research area that focuses on the\ntopological states of classical light. Here we reveal the topological phases\nthat are intrinsic to the particle nature of light, i.e., solely related to the\nquantized Fock states and the inhomogeneous coupling between them. The\nHamiltonian of two cavities coupled with a two-level atom is an intrinsic\none-dimensional Su-Schriefer-Heeger model of Fock states. By adding another\ncavity, the Fock-state lattice is extended to two dimensions with a honeycomb\nstructure, where the strain due to the inhomogeneity of the coupling strengths\ninduces a Lifshitz topological phase transition between a semimetal and a band\ninsulator. In the semimetallic phase, the strain is equivalent to a\npseudomagnetic field, which results in the quantization of the Landau levels\nand the valley Hall effect. We further construct a Haldane model where the\ntopological phases can be characterized by the topological markers. This study\ndemonstrates a fundamental distinction between the topological phases of bosons\nand fermions and provides a novel platform for studying topological physics in\ndimensions higher than three.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Field induced phase segregation and collective excitations of a trapped\n  spinor Bose-Einstein condensate: A hydrodynamic description is used to study the zero-temperature properties\nof a trapped spinor Bose-Einstein condensate in the presence of a uniform\nmagnetic field. We show that, in the case of antiferromagnetic spin-spin\ninteraction, the polar and ferromagnetic configurations of the ground state can\ncoexist in the trap. These two phases are spatially segregated in such a way\nthat the polar state occupies the inner part while the ferromagnetic state\noccupies the outer part of the atomic cloud. We also derive a set of coupled\nhydrodynamic equations for the number density and spin density excitations of\nthe system. It is shown that these equations can be analytically solved for the\nsystem in an isotropic harmonic trap and a constant magnetic field. Remarkably,\nthe related low lying excitation spectra are completely determined by the\nsolutions in the region occupied by the polar state. We find that, within the\nThomas-Fermi approximation, the presence of a constant magnetic field does not\nchange the excitation spectra which still possess the similar form of that\nobtained by Stringari.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Band structure and magnetotransport of a two-dimensional electron gas in\n  the presence of spin-orbit interaction: The band structure and magnetotransport of a two-dimensional electron gas\n(2DEG), in the presence of the Rashba (RSOI) and Dresselhaus (DSOI) terms of\nthe spin-orbit interaction and of a perpendicular magnetic field, is\ninvestigated. Exact and approximate analytical expressions for the band\nstructure are obtained and used to calculate the density of states (DOS) and\nthe longitudinal magnetoresitivity assuming a Gaussian type of level\nbroadening. The interplay between the Zeeman coupling and the two terms of the\nSOI is discussed. If the strengths $\\alpha$ and $ \\beta$, of the RSOI and DSOI,\nrespectively, are equal and the $g$ factor vanishes, the two spin states are\ndegenerate and a shifted Landau-level structure appears. With the increase of\nthe difference $\\alpha- \\beta$, a novel beating pattern of the DOS and of the\nShubnikov-de Haas (SdH) oscillations appears distinctly different from that\noccurring when one of these strengths vanishes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Commensuration torques and lubricity in double moire systems: We study the commensuration torques and layer sliding energetics of\nalternating twist trilayer graphene (t3G) and twisted bilayer graphene on\nhexagonal boron nitride (t2G/BN) that have two superposed moire interfaces.\nLattice relaxations for typical graphene twist angles of $\\sim 1^{\\circ}$ in\nt3G or t2G/BN are found to break the out-of-plane layer mirror symmetry, give\nrise to layer rotation energy local minima dips of the order of $\\sim 10^{-1}$\nmeV/atom at double moire alignment angles, and have sliding energy landscape\nminima between top-bottom layers of comparable magnitude. Moire superlubricity\nis restored for twist angles as small as $\\sim 0.03^\\circ$ away from alignment\nresulting in suppression of sliding energies by several orders of magnitude of\ntypically $\\sim 10^{-4}$ meV/atom, hence indicating the precedence of rotation\nover sliding in the double moire commensuration process.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic field enhancement of organic photovoltaic cells performance: Charge separation is a critical process for achieving high efficiencies in\norganic photovoltaic cells. The initial tightly bound excitonic electron-hole\npair has to dissociate fast enough in order to avoid photocurrent generation\nand thus power conversion efficiency loss via geminate recombination. Such\nprocess takes place assisted by transitional states that lie between the\ninitial exciton and the free charge state. Due to spin conservation rules these\nintermediate charge transfer states typically have singlet character. Here we\npropose a donor-acceptor model for a generic organic photovoltaic cell in which\nthe process of charge separation is modulated by a magnetic field which tunes\nthe energy levels. The impact of a magnetic field is to intensify the\ngeneration of charge transfer states with triplet character via inter-system\ncrossing. As the ground state of the system has singlet character, triplet\nstates are recombination-protected, thus leading to a higher probability of\nsuccessful charge separation. Using the open quantum systems formalism we\ndemonstrate that not only the population of triplet charge transfer states\ngrows in the presence of a magnetic field, but also how the power outcome of an\norganic photovoltaic cell is in that way increased.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Theory of magnetoelectric photocurrent generated by direct interband\n  transitions in semiconductor quantum well: A linearly polarized light normally incident on a semiconductor quantum well\nwith spin-orbit coupling may generate pure spin current via direct interband\noptical transition. An electric photocurrent can be extracted from the pure\nspin current when an in-plane magnetic field is applied, which has been\nrecently observed in the InGaAs/InAlAs quantum well [Dai et al., Phys. Rev.\nLett. 104, 246601 (2010)]. Here we present a theoretical study of this\nmagnetoelectric photocurrent effect associated with the interband transition.\nBy employing the density matrix formalism, we show that the photoexcited\ncarrier density has an anisotropic distribution in k space, strongly dependent\non the orientation of the electron wavevector and the polarization of the\nlight. This anisotropy provides an intuitive picture of the observed dependence\nof the photocurrent on the magnetic field and the polarization of the light. We\nalso show that the ratio of the pure spin photocurrent to the magnetoelectric\nphotocurrent is approximately equal to the ratio of the kinetic energy to the\nZeeman energy, which enables us to estimate the magnitude of the pure spin\nphotocurrent. The photocurrent density calculated with the help of an\nanisotropic Rashba model and the Kohn-Luttinger model can produce all three\nterms in the fitting formula for measured current, with comparable order of\nmagnitude, but discrepancies are still present and further investigation is\nneeded.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Circular edge states in photonic crystals with a Dirac node: Edge states are studied for the two-dimensional Dirac equation in a circular\ngeometry. The properties of the two-component electromagnetic field are\ndiscussed in terms of the three-component polarization field, which can form a\nvortex structure near the Dirac node with a vorticity changing with the sign of\nthe Dirac mass. The Berry curvature of the polarization field is related to the\nBerry curvature of the Dirac spinor state. This quantity is sensitive to a\nchange of boundary conditions. In particular, it vanishes for a geometry with a\nsingle boundary but not for a geometry with two boundaries. This effect is\nrobust against the creation of a step-like edge inside the sample.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Imaging ferroelectric domains with a single-spin scanning quantum sensor: The ability to sensitively image electric fields is important for\nunderstanding many nanoelectronic phenomena, including charge accumulation at\nsurfaces and interfaces and field distributions in active electronic devices. A\nparticularly exciting application is the visualization of domain patterns in\nferroelectric and nanoferroic materials owing to their potential in computing\nand data storage. Here, we use a scanning nitrogen-vacancy (NV) microscope,\nwell known for its use in magnetometry, to image domain patterns in\npiezoelectric (Pb[Zr$_{x}$Ti$_{1-x}$]O$_{3}$) and improper ferroelectric\n(YMnO$_{3}$) materials through their electric fields. Electric field detection\nis enabled by measuring the Stark shift of the NV spin using a gradiometric\ndetection scheme. Analysis of the electric field maps allows us to discriminate\nbetween different types of surface charge distributions, as well as to\nreconstruct maps of the three-dimensional electric field vector and charge\ndensity. The ability to measure both stray electric and magnetic fields under\nambient conditions opens exciting opportunities for the study of multiferroic\nand multifunctional materials and devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interference of magnetointersubband and phonon-induced resistance\n  oscillations in single GaAs quantum wells with two populated subbands: Low-temperature electron magnetotransport in single GaAs quantum wells with\ntwo populated subbands is studied at large filling factors.\nMagneto-inter-subband (MIS) and acoustic-phonon induced oscillations of the\ndissipative resistance are found to be coexisting but interfering substantially\nwith each other. The experiments show that amplitude of the MIS-oscillations\nenhances significantly by phonons, indicating \"constructive interference\"\nbetween the phonon scattering and the intersubband electron transitions.\nTemperature damping of the quantum oscillations is found to be related to\nbroadening of Landau levels caused by considerable electron-electron\nscattering.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Insights on magnon topology and valley-polarization in 2D bilayer\n  quantum magnets: The rich and unconventional physics in layered 2D magnets can open new\navenues for topological magnonics and magnon valleytronics. In particular,\ntwo-dimensional (2D) bilayer quantum magnets are gaining increasing attention\ndue to their intriguing stacking-dependent magnetism, controllable ground\nstates, and topological excitations induced by magnetic spin-orbit couplings\n(SOCs). Despite the substantial research on these materials, their topological\nfeatures remain widely unexplored to date. The present study comprehensively\ninvestigates the magnon topology and magnon valley-polarization in honeycomb\nbilayers with collinear magnetic order. We elucidate the separate and combined\neffects of the SOC, magnetic ground-states, stacking order, and inversion\nsymmetry breaking on the topological phases, magnon valley transport, and the\nHall and Nernst effects. The comprehensive analysis suggests clues to determine\nthe SOC's nature and predicts unconventional Hall and Nernst conductivities in\ntopologically trivial phases. We further report on novel bandgap closures in\nlayered antiferromagnets and detail their topological implications. We believe\nthe present study provides important insights into the fundamental physics and\ntechnological potentials of topological 2D magnons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Signatures of neutral quantum Hall modes in transport through\n  low-density constrictions: Constrictions in fractional quantum Hall (FQH) systems not only facilitate\nbackscattering between counter-propagating edge modes, but also may reduce the\nconstriction filling fraction $\\nu_c$ with respect to the bulk filling fraction\n$\\nu_b$. If both $\\nu_b$ and $\\nu_c$ correspond to incompressible FQH states,\nat least part of the constriction region is surrounded by composite edges,\nwhose low energy dynamics is characterized by a charge mode and one or several\nneutral modes. In the incoherent regime, decay of neutral modes describes the\nequilibration of composite FQH edges, while in the limit of coherent transport,\nthe presence of neutral modes gives rise to universal conductance fluctuations.\nIn addition, neutral modes renormalize the strength of scattering across the\nconstriction, and thus can determine the relative strength of forward and\nbackwards scattering.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Macroscopic Resonant Tunneling through Andreev Interferometers: We investigate the conductance through and the spectrum of ballistic chaotic\nquantum dots attached to two s-wave superconductors, as a function of the phase\ndifference $\\phi$ between the two order parameters. A combination of analytical\ntechniques -- random matrix theory, Nazarov's circuit theory and the\ntrajectory-based semiclassical theory -- allows us to explore the\nquantum-to-classical crossover in detail. When the superconductors are not\nphase-biased, $\\phi=0$, we recover known results that the spectrum of the\nquantum dot exhibits an excitation gap, while the conductance across two normal\nleads carrying $N_{\\rm N}$ channels and connected to the dot via tunnel\ncontacts of transparency $\\Gamma_{\\rm N}$ is $\\propto \\Gamma_{\\rm N}^2 N_{\\rm\nN}$. In contrast, when $\\phi=\\pi$, the excitation gap closes and the\nconductance becomes $G \\propto \\Gamma_{\\rm N} N_{\\rm N}$ in the universal\nregime. For $\\Gamma_{\\rm N} \\ll 1$, we observe an order-of-magnitude\nenhancement of the conductance towards $G \\propto N_{\\rm N}$ in the\nshort-wavelength limit. We relate this enhancement to resonant tunneling\nthrough a macroscopic number of levels close to the Fermi energy. Our\npredictions are corroborated by numerical simulations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Synthesis of Graphene on Gold: Here we report chemical vapor deposition of graphene on gold surface at\nambient pressure. We studied effects of the growth temperature, pressure and\ncooling process on the grown graphene layers. The Raman spectroscopy of the\nsamples reveals the essential properties of the graphene grown on gold surface.\nIn order to characterize the electrical properties of the grown graphene\nlayers, we have transferred them on insulating substrates and fabricated field\neffect transistors. Owing to distinctive properties of gold, the ability to\ngrow graphene layers on gold surface could open new applications of graphene in\nelectrochemistry and spectroscopy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effects of substrate corrugation during helium adsorption on graphene in\n  the grand canonical ensemble: Adsorption of 4He on atomically flat substrates such as graphene provides a\nroute towards the engineering of low dimensional quantum phases including\nsuperfluids and strongly interacting insulators. In this study, we explore the\neffects of graphene corrugation on the helium adsorption process via quantum\nMonte Carlo simulations in the grand canonical ensemble. We utilize an\nempirical adsorption potential based on the superposition of individual\nhelium-carbon interactions and systematically control corrugation, from a\nsmooth membrane to the fully rough potential, via the implementation of a\ncutoff in reciprocal space. The results highlight the importance of using a\nfully corrugated potential to understand the plethora of commensurate and\nincommensurate phases in the first adsorbed layer. Surprisingly, some residual\neffects of corrugation are still present before and during the promotion and\nonset of a second adsorbed layer, where a smooth adsorption can lead to\nenhanced particle fluctuations in a helium-interaction dominated regime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Gibbs phenomenon and the emergence of the steady-state in quantum\n  transport: Simulations are increasingly employing explicit reservoirs - internal, finite\nregions - to drive electronic or particle transport. This naturally occurs in\nsimulations of transport via ultracold atomic gases. Whether the simulation is\nnumerical or physical, these approaches rely on the rapid development of the\nsteady state. We demonstrate that steady state formation is a manifestation of\nthe Gibbs phenomenon well-known in signal processing and in truncated discrete\nFourier expansions. Each particle separately develops into an individual steady\nstate due to the spreading of its wave packet in energy. The rise to the steady\nstate for an individual particle depends on the particle energy - and thus can\nbe slow - and ringing oscillations appear due to filtering of the response\nthrough the electronic bandwidth. However, the rise to the total steady state -\nthe one from all particles - is rapid, with timescale $\\pi/W$, where $W$ is the\nbandwidth. Ringing oscillations are now also filtered through the bias window,\nand they decay with a higher power. The Gibbs constant - the overshoot of the\nfirst ring - can appear in the simulation error. These results shed light on\nthe formation of the steady state and support the practical use of explicit\nreservoirs to simulate transport at the nanoscale or using ultracold atomic\nlattices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Subgap dynamics of double quantum dot coupled between superconducting\n  and normal leads: Dynamical processes induced by the external time-dependent fields can provide\nvaluable insight into the characteristic energy scales of a given physical\nsystem. We investigate them here in a nanoscopic heterostructure, consisting of\nthe double quantum dot coupled in series to the superconducting and the\nmetallic reservoirs, analyzing its response to (i)~abrupt bias voltage applied\nacross the junction, (ii) sudden change of the energy levels, and imposed by\n(iii)~their periodic driving. We explore subgap properties of this setup which\nare strictly related to the in-gap quasiparticles and discuss their signatures\nmanifested in the time-dependent charge currents. The characteristic multi-mode\noscillations, their beating patters and photon-assisted harmonics reveal a rich\nspectrum of dynamical features that might be important for designing the\nsuperconducting qubits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Parametric symmetry breaking in a nonlinear resonator: Much of the physical world around us can be described in terms of harmonic\noscillators in thermodynamic equilibrium. At the same time, the far from\nequilibrium behavior of oscillators is important in many aspects of modern\nphysics. Here, we investigate a resonating system subject to a fundamental\ninterplay between intrinsic nonlinearities and a combination of several driving\nforces. We have constructed a controllable and robust realization of such a\nsystem using a macroscopic doubly clamped string. We experimentally observe a\nhitherto unseen double hysteresis in both the amplitude and the phase of the\nresonator's response function and present a theoretical model that is in\nexcellent agreement with the experiment. Our work provides a thorough\nunderstanding of the double-hysteretic response through a symmetry breaking of\nparametric phase states that elucidates the selection criteria governing\ntransitions between stable solutions. Our study motivates applications ranging\nfrom ultrasensitive force detection to low-energy computing memory units.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Time-Loop Formalism for Irreversible Quantum Problems: Steady State\n  Transport in Junctions with Asymmetric Dynamics: Non-unitary quantum mechanics has been used in the past to study\nirreversibility, dissipation and decay in a variety of physical systems. In\nthis letter, we propose a general scheme to deal with systems governed by\nnon-Hermitian Hamiltonians. We argue that the Schwinger-Keldysh formalism gives\na natural description for those problems. To elucidate the method, we study a\nsimple model inspired by mesoscopic physics --an asymmetric junction. The\nsystem is governed by a non-Hermitian Hamiltonian which captures essential\naspects of irreversibility.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Charge puddles in the bulk and on the surface of the topological\n  insulator BiSbTeSe$_2$ studied by scanning tunneling microscopy and optical\n  spectroscopy: The topological insulator BiSbTeSe$_2$ corresponds to a compensated\nsemiconductor in which strong Coulomb disorder gives rise to the formation of\ncharge puddles, i.e., local accumulations of charge carriers, both in the bulk\nand on the surface. Bulk puddles are formed if the fluctuations of the Coulomb\npotential are as large as half of the band gap. The gapless surface, in\ncontrast, is sensitive to small fluctuations but the potential is strongly\nsuppressed due to the additional screening channel provided by metallic surface\ncarriers. To study the quantitative relationship between the properties of bulk\npuddles and surface puddles, we performed infrared transmittance measurements\nas well as scanning tunneling microscopy measurements on the same sample of\nBiSbTeSe$_2$, which is close to perfect compensation. At 5.5 K, we find surface\npotential fluctuations occurring on a length scale $r_s = 40-50$ nm with\namplitude $\\Gamma = 8-14$ meV which is much smaller than in the bulk, where\noptical measurements detect the formation of bulk puddles. In this nominally\nundoped compound, the value of $\\Gamma$ is smaller than expected for pure\nscreening by surface carriers, and we argue that this arises most likely from a\ncooperative effect of bulk screening and surface screening.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic-field asymmetry of nonlinear mesoscopic transport: We investigate departures of the Onsager relations in the nonlinear regime of\nelectronic transport through mesoscopic systems. We show that the nonlinear\ncurrent--voltage characteristic is not an even function of the magnetic field\ndue only to the magnetic-field dependence of the screening potential within the\nconductor. We illustrate this result for two types of conductors: A quantum\nHall bar with an antidot and a chaotic cavity connected to quantum point\ncontacts. For the chaotic cavity we obtain through random matrix theory an\nasymmetry in the fluctuations of the nonlinear conductance that vanishes\nrapidly with the size of the contacts.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Direct Bandgap Emission from Hexagonal Ge and SiGe Alloys: Silicon crystallized in the usual cubic (diamond) lattice structure has\ndominated the electronics industry for more than half a century. However, cubic\nsilicon (Si), germanium (Ge) and SiGe-alloys are all indirect bandgap\nsemiconductors that cannot emit light efficiently. Accordingly, achieving\nefficient light emission from group-IV materials has been a holy grail in\nsilicon technology for decades and, despite tremendous efforts, it has remained\nelusive. Here, we demonstrate efficient light emission from direct bandgap\nhexagonal Ge and SiGe alloys. We measure a subnanosecond,\ntemperature-insensitive radiative recombination lifetime and observe a similar\nemission yield to direct bandgap III-V semiconductors. Moreover, we demonstrate\nhow by controlling the composition of the hexagonal SiGe alloy, the emission\nwavelength can be continuously tuned in a broad range, while preserving a\ndirect bandgap. Our experimental findings are shown to be in excellent\nquantitative agreement with the ab initio theory. Hexagonal SiGe embodies an\nideal material system to fully unite electronic and optoelectronic\nfunctionalities on a single chip, opening the way towards novel device concepts\nand information processing technologies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Particle tunneling through a polarizable insulator: The tunneling probability between two leads connected by a molecule, a chain,\na film, or a bulk polarizable insulator is investigated within a model of an\nelectron tunneling from lead A to a state higher in energy, describing the\nbarrier, and from there to lead B. To describe the possibility of energy\nexchange with excitations of the molecule or the insulator we couple the\nintermediate state to a single oscillator or to a spectrum of these,\nrespectively. In the single-oscillator case we find for weak coupling that the\ntunneling is weakly suppressed by a Debye-Waller-type factor. For stronger\ncoupling the oscillator gets 'stiff' and we observe a suppression of tunneling\nsince the effective barrier is increased. The probability for the electron to\nexcite the oscillator increases with the coupling. In the case of a film, or a\nbulk barrier the behavior is qualitatively the same as in the single oscillator\ncase. An insulating chain, as opposed to a film or a bulk connecting the two\nleads,shows an 'orthogonality catastrophe' similar to that of an electronic\ntransition in a Fermi gas.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Influence of Landau level mixing on the properties of elementary\n  excitations in graphene in strong magnetic field: Massless Dirac electrons in graphene fill Landau levels with energies scaled\nas square roots of their numbers. Coulomb interaction between electrons leads\nto mixing of different Landau levels. The relative strength of this interaction\ndepends only on dielectric susceptibility of surrounding medium and can be\nlarge in suspended graphene. We consider influence of Landau level mixing on\nthe properties of magnetoexcitons and magnetoplasmons - elementary\nelectron-hole excitations in graphene in quantizing magnetic field. We show\nthat, at small enough background dielectric screening, the mixing leads to very\nessential change of magnetoexciton and magnetoplasmon dispersion laws in\ncomparison with the lowest Landau level approximation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Colossal orbital Zeeman effect driven by tunable spin-Berry curvature in\n  a kagome metal: Berry phase and the related concept of Berry curvature can give rise to many\nunconventional phenomena in solids. In this work, we discover colossal orbital\nZeeman effect of topological origin in a newly synthesized bilayer kagome metal\nTbV6Sn6. We use spectroscopic-imaging scanning tunneling microscopy to study\nthe magnetic field induced renormalization of the electronic band structure.\nThe nonmagnetic vanadium d-orbitals form Dirac crossings at the K point with a\nsmall mass gap and strong Berry curvature induced by the spin-orbit coupling.\nWe reveal that the magnetic field leads to the splitting of gapped Dirac\ndispersion into two branches with giant momentum-dependent g factors, resulting\nin the substantial renormalization of the Dirac band. These measurements\nprovide a direct observation of the magnetic field controlled orbital Zeeman\ncoupling to the enormous orbital magnetic moments of up to 200 Bohr magnetons\nnear the gapped Dirac points. Interestingly, the effect is increasingly\nnon-linear, and becomes gradually suppressed at higher magnetic fields.\nTheoretical modeling further confirms the existence of orbital magnetic moments\nin TbV6Sn6 produced by the non-trivial spin-Berry curvature of the Bloch wave\nfunctions. Our work provides the first direct insight into the\nmomentum-dependent nature of topological orbital moments and their tunability\nby magnetic field concomitant with the evolution of the spin-Berry curvature.\nSignificantly large orbital magnetic moments driven by the Berry curvature can\nalso be generated by other quantum numbers beyond spin, such as the valley in\ncertain graphene-based structures, which may be unveiled using the same tools\nhighlighted in our work.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Reversible Single Spin Control of Individual Magnetic Molecule by\n  Hydrogen Atom Adsorption: The reversible control of a single spin of an atom or a molecule is of great\ninterest in Kondo physics and a potential application in spin based\nelectronics.Here we demonstrate that the Kondo resonance of manganese\nphthalocyanine molecules on an Au(111) substrate have been reversibly switched\noff and on via a robust route through attachment and detachment of single\nhydrogen atom to the magnetic core of the molecule. As further revealed by\ndensity functional theory calculations, even though the total number of\nelectrons of the Mn ion remains almost the same in the process, gaining one\nsingle hydrogen atom leads to redistribution of charges within 3d orbitals with\na reduction of the molecular spin state from S = 3/2 to S = 1 that directly\ncontributes to the Kondo resonance disappearance. This process is reversed by a\nlocal voltage pulse or thermal annealing to desorb the hydrogen atom.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-Markovian electron dynamics in nanostructures coupled to dissipative\n  contacts: In quasiballistic semiconductor nanostructures, carrier exchange between the\nactive region and dissipative contacts is the mechanism that governs\nrelaxation. In this paper, we present a theoretical treatment of transient\nquantum transport in quasiballistic semiconductor nanostructures, which is\nbased on the open system theory and valid on timescales much longer than the\ncharacteristic relaxation time in the contacts. The approach relies on a model\ninteraction between the current-limiting active region and the contacts, given\nin the scattering-state basis. We derive a non-Markovian master equation for\nthe irreversible evolution of the active region's many-body statistical\noperator by coarse-graining the exact dynamical map over the contact relaxation\ntime. In order to obtain the response quantities of a nanostructure under bias,\nsuch as the potential and the charge and current densities, the non-Markovian\nmaster equation must be solved numerically together with the Schr\\\"{o}dinger,\nPoisson, and continuity equations. We discuss how to numerically solve this\ncoupled system of equations and illustrate the approach on the example of a\nsilicon nin diode.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-splitting in the quantum Hall effect of disordered GaAs layers with\n  strong overlap of the spin subbands: With minima in the diagonal conductance G_{xx} and in the absolute value of\nthe derivative |dG_{xy}/dB| at the Hall conductance value G_{xy}=e^{2}/h,\nspin-splitting is observed in the quantum Hall effect of heavily Si-doped GaAs\nlayers with low electron mobility 2000 cm^2/Vs in spite of the fact that the\nspin-splitting is much smaller than the level broadening. Experimental results\ncan be explained in the frame of the scaling theory of the quantum Hall effect,\napplied independently to each of the two spin subbands.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Realization of bulk insulating property and carrier manipulation in\n  reversible spin current regime of the ideal topological insulator TlBiSe2: The surfaces of three-dimensional topological insulators (TIs) characterized\nby a spin-helical Dirac fermion provide a fertile ground for realizing exotic\nphenomena as well as having potential for wide-ranging applications. To realize\nmost of their special properties, the Dirac point (DP) is required to be\nlocated near the Fermi energy with a bulk insulating property while it is\nhardly achieved in most of the discovered TIs. It has been recently found that\nTlBiSe2 features an in-gap DP, where upper and lower parts of surface Dirac\ncone are both utilized. Nevertheless, investigations of the surface transport\nproperties of this material are limited due to the lack of bulk insulating\ncharacteristics. Here, we present the first realization of bulk insulating\nproperty by tuning the composition of Tl1-xBi1+xSe2-d without introducing guest\natoms that can bring the novel properties into the reality. This result\npromises to shed light on new exotic topological phenomena on the surface.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Efficient Computation of Kubo Conductivity for Incommensurate 2D\n  Heterostructures: Here we introduce a numerical method for computing conductivity via the Kubo\nFormula for incommensurate 2D bilayer heterostructures using a tight-binding\nframework. We begin with deriving the momentum space formulation and Kubo\nFormula from the real space tight-binding model using the appropriate Bloch\ntransformation operator. We further discuss the resulting algorithm along with\nits convergence rate and computation cost in terms of parameters such as\nrelaxation time and temperature. In particular, we show that for low\nfrequencies, low temperature, and long relaxation times conductivity can be\ncomputed very efficiently using momentum space for a wide class of materials.\nWe then demonstrate our method by computing conductivity for twisted bilayer\ngraphene (tBLG) for small twist angles.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Universal quantum computation on a semiconductor quantum wire network: Universal quantum computation (UQC) using Majorana fermions on a 2D\ntopological superconducting (TS) medium remains an outstanding open problem.\nThis is because the quantum gate set that can be generated by braiding of the\nMajorana fermions does not include \\emph{any} two-qubit gate and also the\nsingle-qubit $\\pi/8$ phase gate. In principle, it is possible to create these\ncrucial extra gates using quantum interference of Majorana fermion currents.\nHowever, it is not clear if the motion of the various order parameter defects\n(vortices, domain walls, \\emph{etc.}), to which the Majorana fermions are bound\nin a TS medium, can be quantum coherent. We show that these obstacles can be\novercome using a semiconductor quantum wire network in the vicinity of an\n$s$-wave superconductor, by constructing topologically protected two-qubit\ngates and any arbitrary single-qubit phase gate in a topologically unprotected\nmanner, which can be error corrected using magic state distillation. Thus our\nstrategy, using a judicious combination of topologically protected and\nunprotected gate operations, realizes UQC on a quantum wire network with a\nremarkably high error threshold of $0.14$ as compared to $10^{-3}$ to $10^{-4}$\nin ordinary unprotected quantum computation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Controlling Hot Electron Spatial and Momentum Distributions in\n  Nanoplasmonic Systems: Volume versus Surface Effects: Hot carrier spatial and momentum distributions in nanoplasmonic systems\ndepend sensitively on the optical excitation parameters and nanoscale geometry,\nwhich therefore determine the efficiency and functionality of plasmon-enhanced\ncatalysts, photovoltaics, and nanocathodes. A growing appreciation over the\npast decade for the distinction between volume- and surface-mediated\nphotoexcitation and electron emission from such systems has underscored the\nneed for direct mechanistic insight and quantification of these two processes.\nToward this end, we use angle-resolved photoelectron velocity mapping to\ndirectly distinguish volume and surface contributions to nanoplasmonic hot\nelectron emission from gold nanorods as a function of aspect ratio, down to the\nspherical limit. Nanorods excited along their longitudinal surface plasmon axis\nexhibit surprising transverse photoemission distributions due to the dominant\nvolume excitation mechanisms, as reproduced via ballistic Monte Carlo\nmodelling. We further demonstrate a screening-induced transition from volume\n(transverse) to surface (longitudinal) photoemission with red detuning of the\nexcitation laser and determine the relative cross-sections of the two\nmechanisms via combined volume and surface multiphoton photoemission modelling.\nBased on these results, we are able to identify geometry- and material-specific\ncontributions to the photoemission cross-sections and offer general principles\nfor designing nanoplasmonic systems to control hot electron excitation and\nemission distributions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Theory of defect dynamics in graphene: defect groupings and their\n  stability: We use our theory of periodized discrete elasticity to characterize defects\nin graphene as the cores of dislocations or groups of dislocations. Earlier\nnumerical implementations of the theory predicted some of the simpler defect\ngroupings observed in subsequent Transmission Electron Microscope experiments.\nHere we derive the more complicated defect groupings of three or four defect\npairs from our theory, show that they correspond to the cores of two pairs of\ndislocation dipoles and ascertain their stability.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Understanding the structure of the first atomic contact in Gold: We have studied experimentally the phenomena of jump-to-contact (JC) and\njump-out-of-contact (JOC) in gold electrodes. JC can be observed at the first\ncontact when the two metals approach each other while JOC occurs in the last\ncontact before breaking. When the indentation depth between the electrodes is\nlimited to a certain value of conductance, a highly reproducible behaviour in\nthe evolution of the conductance can be obtained for hundreds of cycles of\nformation and rupture. Molecular dynamics simulations of this process show how\nthe two metallic electrodes are shaped into tips of a well-defined\ncrystallographic structure formed through a mechanical annealing mechanism. We\nreport a detailed analysis of the atomic configurations obtained before contact\nand rupture of these stable structures and obtained their conductance using\nfirst-principlesquantum transport calculations. These results help us\nunderstand the values of conductance obtained experimentally in the JC and JOC\nphenomena and improve our understanding of atomic-sized contacts and the\nevolution of their structural characteristics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Correlation and dephasing effects on the non-radiative coherence between\n  bright excitons in an InAs QD ensemble measured with 2D spectroscopy: Exchange-mediated fine-structure splitting of bright excitons in an ensemble\nof InAs quantum dots is studied using optical two-dimensional Fourier-transform\nspectroscopy. By monitoring the non-radiative coherence between the bright\nstates, we find that the fine-structure splitting decreases with increasing\nexciton emission energy at a rate of 0.1 $\\mu$eV/meV. Dephasing rates are\ncompared to population decay rates to reveal that pure dephasing causes the\nexciton optical coherences to decay faster than the radiative limit at low\ntemperature, independent of excitation density. Fluctuations of the bright\nstate transition energies are nearly perfectly-correlated, protecting the\nnon-radiative coherence from interband dephasing mechanisms.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Surface twist instabilities and skyrmion states in chiral ferromagnets: In epitaxial MnSi/Si(111) films, the in-plane magnetization saturation is\nnever reached due to the formation of specific surface chiral modulations with\nthe propagation direction perpendicular to the film surfaces [Wilson et al.\nPhys. Rev. B 88, 214420 (2013)]. In this paper we show that the occurrence of\nsuch chiral surface twists is a general effect attributed to all bulk and con-\nfined magnetic crystals lacking inversion symmetry. We present experimental\ninvestigations of this phenomenon in nanolayers of MnSi/Si(111) supported by\ndetailed theoretical analysis within the standard phenomenological model. In\nmagnetic nanolayers with intrinsic or induced chirality, such surface induced\ninstabilities become sizeable effects and play a crucial role in the formation\nof skyrmion lattices and other nontrivial chiral modulations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The origin of the core-level binding energy shifts in nanoclusters: We investigate the shifts of the core-level binding energies in small gold\nnanoclusters by using {\\it ab initio} density functional theory calculations.\nThe shift of the 4$f$ states is calculated for magic number nanoclusters in a\nwide range of sizes and morphologies. We find a non-monotonous behavior of the\ncore-level shift in nanoclusters depending on the size. We demonstrate that\nthere are three main contributions to the Au 4$f$ shifts, which depend\nsensitively on the interatomic distances, coordination and quantum confinement.\nThey are identified and explained by the change of the on-site electrostatic\npotential.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Long-range Kitaev Chains via Planar Josephson Junctions: We show how a recently proposed solid state Majorana platform comprising a\nplanar Josephson junction proximitized to a 2D electron gas (2DEG) with Rashba\nspin-orbit coupling and Zeeman field can be viewed as an effectively one\ndimensional (1D) Kitaev chain with long-range pairing and hopping terms. We\nhighlight how the couplings of the 1D system may be tuned by changing\nexperimentally realistic parameters. We also show that the mapping is robust to\ndisorder by computing the Clifford pseudospectrum index in real space for the\nlong-range Kitaev chain across several topological phases. This mapping opens\nup the possibility of using current experimental setups to explore 1D\ntopological superconductors with non-standard, and tunable couplings.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Temperature evolution of the quantum Hall effect in the FISDW state:\n  Theory vs Experiment: We discuss the temperature dependence of the Hall conductivity $\\sigma_{xy}$\nin the magnetic-field-induced spin-density-wave (FISDW) state of the\nquasi-one-dimensional Bechgaard salts (TMTSF)_2X. Electronic thermal\nexcitations across the FISDW energy gap progressively destroy the quantum Hall\neffect, so $\\sigma_{xy}(T)$ interpolates between the quantized value at zero\ntemperature and zero value at the transition temperature T_c, where FISDW\ndisappears. This temperature dependence is similar to that of the superfluid\ndensity in the BCS theory of superconductivity. More precisely, it is the same\nas the temperature dependence of the Fr\\\"ohlich condensate density of a regular\nCDW/SDW. This suggests a two-fluid picture of the quantum Hall effect, where\nthe Hall conductivity of the condensate is quantized, but the condensate\nfraction of the total electron density decreases with increasing temperature.\nThe theory appears to agree with the experimental results obtained by measuring\nall three components of the resistivity tensor simultaneously on a\n(TMTSF)_2PF_6 sample and then reconstructing the conductivity tensor.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Accessing the anisotropic non-thermal phonon populations in black\n  phosphorus: We combine femtosecond electron diffuse scattering experiments and\nfirst-principles calculations of the coupled electron-phonon dynamics to\nprovide a detailed momentum-resolved picture of the ultrafast lattice\nthermalization in a thin film of black phosphorus. The measurements reveal the\nemergence of highly anisotropic non-thermal phonon populations which persist\nfor several picoseconds following excitation of the electrons with a light\npulse. Combining ultrafast dynamics simulations based on the time-dependent\nBoltzmann formalism and calculations of the structure factor, we reproduce the\nexperimental data and identify the vibrational modes primarily responsible for\nthe carrier relaxation via electron-phonon coupling and the subsequent lattice\nthermalization via phonon-phonon scattering. In particular, we attribute the\nnon-equilibrium lattice dynamics of black phosphorus to highly-anisotropic\nphonon-assisted scattering processes, which are primarily mediated by\nhigh-energy optical phonons. Our approach paves the way towards unravelling and\ncontrolling microscopic energy-flow pathways in two-dimensional materials and\nvan der Waals heterostructures, and may also be extended to other\nnon-equilibrium phenomena involving coupled electron-phonon dynamics such as\nsuperconductivity, phase transitions or polaron physics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electrostatic quantum dot confinement in phosphorene: We consider states localized by electrostatic potentials in phosphorene using\nan atomistic tight binding approach. From the results of the tight-binding\ncalculations of the confined states we extract effective masses for the\nconduction band electrons in the armchair and zigzag directions. The masses\nderived in this way are used for a simple single-band effective mass model\nwhich, as we find, reproduces very well the tight-binding energy spectrum in\nexternal magnetic field, the probability densities and the interaction effects.\nBoth methods produce Wigner crystallization for the ground-state of the\nelectron pair with the single-electron islands separated in the armchair\ndirection already for small quantum dots.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Asymmetric power dissipation in electronic transport through a quantum\n  point contact: We investigate the power dissipated by an electronic current flowing through\na quantum point contact in a two-dimensional electron gas. Based on the\nLandauer-B\\\"uttiker approach to quantum transport, we evaluate the power that\nis dissipated on the two sides of the constriction as a function of the Fermi\nenergy, temperature, and applied voltage. We demonstrate that an asymmetry\nappears in the dissipation, which is most pronounced when the quantum point\ncontact is tuned to a conductance step where the transmission strongly depends\non energy. At low temperatures, the asymmetry is enhanced when the temperature\nincreases. An estimation for the position of the maximum dissipation is\nprovided.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron states in the quantum wire with periodic serial structure: A model quantum wire embedded in a matrix permeable to electron waves is\ninvestigated in terms of electronic states. The wire is assumed to have a 1D\ncrystal structure. Through electron waves propagating in its surroundings,\nlateral modes are coupled with Bloch waves propagating along the wire axis,\nwhich results in modes splitting into multiplets. The results presented in this\nstudy have been obtained by direct solution of the Schrodinger equation in the\neffective mass approximation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Subgap features due to quasiparticle tunneling in quantum dots coupled\n  to superconducting leads: We present a microscopic theory of transport through quantum dot set-ups\ncoupled to superconducting leads. We derive a master equation for the reduced\ndensity matrix to lowest order in the tunneling Hamiltonian and focus on\nquasiparticle tunneling. For high enough temperatures transport occurs in the\nsubgap region due to thermally excited quasiparticles, which can be used to\nobserve excited states of the system for low bias voltages. On the example of a\ndouble quantum dot we show how subgap transport spectroscopy can be done.\nMoreover, we use the single level quantum dot coupled to a normal and a\nsuperconducting lead to give a possible explanation for the subgap features\nobserved in the experiments published in Appl. Phys. Lett. 95, 192103 (2009).",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Atomic relaxation and electronic structure in twisted bilayer MoS2 with\n  rotation angle of 5.09 degrees: It is now well established theoretically and experimentally that a moir\\'e\npattern, due to a rotation of two atomic layers with respect to each other,\ncreates low-energy flat bands. First discovered in twisted bilayer graphene,\nthese new electronic states are at the origin of strong electronic correlations\nand even of unconventional superconductivity. Twisted bilayers (tb) of\ntransition metal dichalcogenides (TMDs) also exhibit flat bands around their\nsemiconductor gap at small rotation angles. In this paper, we present a DFT\nstudy to analyze the effect of the atomic relaxation on the low-energy bands of\ntb-MoS2 with a rotation angle of 5.09 degrees. We show that in-plane atomic\nrelaxation is not essential here, while out-of-plane relaxation dominates the\nelectronic structure. We propose a simple and efficient atomic model to predict\nthis relaxation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Entanglement in Nanocavity Arrays: We show theoretically how quantum interference between linearly coupled modes\nwith weak local nonlinearity allows the generation of continuous variable\nentanglement. By solving the quantum master equation for the density matrix, we\nshow how the entanglement survives realistic levels of pure dephasing. The\ngeneration mechanism forms a new paradigm for entanglement generation in arrays\nof coupled quantum modes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Disorder and localization effects on the local spectroscopic and\n  infrared-optical properties of $\\mbox{Ga}_{1-x}\\mbox{Mn}_x\\mbox{As}$: We study numerically the influence of disorder and localization effects on\nthe local spectroscopic characteristics and infrared optical properties of\n$\\mbox{Ga}_{1-x}\\mbox{Mn}_x\\mbox{As}$. We treat the band structure and disorder\neffects at an equal level by using exact diagonalization supercell simulation\nmethod. This method accurately describes the low doping limit and gives a clear\npicture of the transition to higher dopings, which captures the localization\neffects inaccessible to other theoretical methods commonly used. Our\nsimulations capture the rich mid-gap localized states observed in scanning\ntunneling microscopy studies and reproduce the observed features of the\ninfrared optical absorption experiments. We show clear evidence of a disordered\nvalence band model for metallic samples in which (i) there is no impurity band\ndetached from the valence band, (ii) the disorder tends to localize and pull\nstates near the top of the valence band into the gap region, and (iii) the\nFermi energy is located deep in the delocalized region away from the mobility\nedge. We identify localized states deep in the gap region by visualizing the\nprobability distribution of the quasiparticles and connecting it to their\nrespective participation ratios. The analysis of the infrared-optical\nabsorption data indicates that it does not have a direct relation to the nature\nof the states at the Fermi energy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Limitations of the kinetic theory to describe the near-field heat\n  exchanges in many-body systems: We investigate the radiative heat transfer along a chain of nanoparticles\nusing both a purely kinetic approach based on the solution of a Boltzmann\ntransport equation and an exact method (Landauer's approach) based on\nfluctuational electrodynamics. We show that the kinetic theory generally fails\nto predict properly the heat flux transported along the chain both at close\n(near-field regime) and large separation (far-field regime) distances. We\nreport a deviation of a factor two between the heat fluxes predicted by the two\napproaches in the diffusive regime of heat transport and we show that this\ndifference becomes even greater than two orders of magnitude in the ballistic\nregime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "2D massless QED Hall half-integer conductivity and graphene: Starting from the photon self-energy tensor in a magnetized medium, the 3D\ncomplete antisymmetric form of the conductivity tensor is found in the static\nlimit of a fermion system $C$ non-invariant under fermion-antifermion exchange.\nThe massless relativistic 2D fermion limit in QED is derived by using the\ncompactification along the dimension parallel to the magnetic field. In the\nstatic limit and at zero temperature the main features of quantum Hall effect\n(QHE) are obtained: the half-integer QHE and the minimum value proportional to\n$e^2/h$ for the Hall conductivity . For typical values of graphene the plateaus\nof the Hall conductivity are also reproduced.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Conductance Quantization and Magnetoresistance in Magnetic Point\n  Contacts: We theoretically study the electron transport through a magnetic point\ncontact (PC) with special attention to the effect of an atomic scale domain\nwall (DW). The spin precession of a conduction electron is forbidden in such an\natomic scale DW and the sequence of quantized conductances depends on the\nrelative orientation of magnetizations between left and right electrodes. The\nmagnetoresistance is strongly enhanced for the narrow PC and oscillates with\nthe conductance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-thermopower in interacting quantum dots: Using analytical arguments and the numerical renormalization group method we\ninvestigate the spin-thermopower of a quantum dot in a magnetic field. In the\nparticle-hole symmetric situation the temperature difference applied across the\ndot drives a pure spin current without accompanying charge current. For\ntemperatures and fields at or above the Kondo temperature, but of the same\norder of magnitude, the spin-Seebeck coefficient is large, of the order of\nk_B/e. Via a mapping, we relate the spin-Seebeck coefficient to the\ncharge-Seebeck coefficient of a negative-U quantum dot where the corresponding\nresult was recently reported by Andergassen et al. in Phys. Rev. B 84, 241107\n(2011). For several regimes we provide simplified analytical expressions. In\nthe Kondo regime, the dependence of the spin-Seebeck coefficient on the\ntemperature and the magnetic field is explained in terms of the shift of the\nKondo resonance due to the field and its broadening with the temperature and\nthe field. We also consider the influence of breaking the particle-hole\nsymmetry and show that a pure spin current can still be realized provided a\nsuitable electric voltage is applied across the dot. Then, except for large\nasymmetries, the behavior of the spin-Seebeck coefficient remains similar to\nthat found in the particle-hole symmetric point.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A new kind of 2D topological insulators BiCN with a giant gap and its\n  substrate effects: Based on DFT calculation, we predict that BiCN, i.e., bilayer Bi films\npassivated with -CN group, is a novel 2D Bi-based material with highly\nthermodynamic stability, and demonstrate that it is also a new kind of 2D TI\nwith a giant SOC gap (? 1 eV) by direct calculation of the topological\ninvariant Z2 and obvious exhibition of the helical edge states. Monolayer h-BN\nand MoS2 are identified as good candidate substrates for supporting the\nnontrivial topological insulating phase of the 2D TI films, since the two\nsubstrates can stabilize and weakly interact with BiCN via van derWaals\ninteraction and thus hardly affect the electronic properties, especially the\nband topology. The topological properties are robust against the strain and\nelectric field. This may provide a promising platform for realization of novel\ntopological phases.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Discovery of highly spin-polarized conducting surface states in the\n  strong spin-orbit coupling semiconductor Sb$_2$Se$_3$: Majority of the A$_2$B$_3$ type chalcogenide systems with strong spin-orbit\ncoupling, like Bi$_2$Se$_3$, Bi$_2$Te$_3$ and Sb$_2$Te$_3$ etc., are\ntopological insulators. One important exception is Sb$_2$Se$_3$, where a\ntopological non-trivial phase was argued to be possible under ambient\nconditions, but such a phase could be detected to exist only under pressure. In\nthis Letter, we show that like Bi$_2$Se$_3$, Sb$_2$Se$_3$, displays generation\nof highly spin-polarized current under mesoscopic superconducting point\ncontacts as measured by point contact Andreev reflection spectroscopy. In\naddition, we observe a large negative and anisotropic magnetoresistance in\nSb$_2$Se$_3$, when the field is rotated in the basal plane. However, unlike in\nBi$_2$Se$_3$, in case of Sb$_2$Se$_3$ a prominent quasiparticle interference\n(QPI) pattern around the defects could be obtained in STM conductance imaging.\nThus, our experiments indicate that Sb$_2$Se$_3$ is a regular band insulator\nunder ambient conditions, but due to it's high spin-orbit coupling, non-trivial\nspin-texture exists on the surface and the system could be on the verge of a\ntopological insulator phase.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-Hermitian boundary and interface states in nonreciprocal\n  higher-order topological metals and electrical circuits: Non-Hermitian skin-edge states emerge only at one edge in one-dimensional\nnonreciprocal chains, where all states are localized at the edge irrespective\nof eigenvalues. The bulk topological number is the winding number associated\nwith the complex energy spectrum, which is well defined for metals. We study\nnon-Hermitian nonreciprocal systems in higher dimensions, and propose to\nrealize them with the use of electric diode circuits. We first investigate\none-dimensional interface states between two domains carrying different\ntopological numbers, where all states are localized at the interface. They are\na generalization of the skin-edge states. Then we generalize them into higher\ndimensions. We show that there emerge a rich variety of boundary states and\ninterface states including surface, line and point states in three-dimensional\nsystems. They emerge at boundaries of several domains carrying different\ntopological numbers. The resulting systems are the first-order, second-order\nand third-order topological metals. Such states may well be observed by\nmeasuring the two-point impedance in diode circuits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Graphene wormholes: A condensed matter illustration of Dirac fermions in\n  curved space: We study the properties of graphene wormholes in which a short nanotube acts\nas a bridge between two graphene sheets, where the honeycomb carbon lattice is\ncurved from the presence of 12 heptagonal defects. By taking the nanotube\nbridge with very small length compared to the radius, we develop an effective\ntheory of Dirac fermions to account for the low-energy electronic properties of\nthe wormholes in the continuum limit, where the frustration induced by the\nheptagonal defects is mimicked by a line of fictitious gauge flux attached to\neach of them. We find in particular that, when the effective gauge flux from\nthe topological defects becomes maximal, the zero-energy modes of the Dirac\nequation can be arranged into two triplets, that can be thought as the\ncounterpart of the two triplets of zero modes that arise in the dual instance\nof the continuum limit of large spherical fullerenes. We further investigate\nthe graphene wormhole spectra by performing a numerical diagonalization of\ntight-binding hamiltonians for very large lattices realizing the wormhole\ngeometry. The correspondence between the number of localized electronic states\nobserved in the numerical approach and the effective gauge flux predicted in\nthe continuum limit shows that graphene wormholes can be consistently described\nby an effective theory of two Dirac fermion fields in the curved geometry of\nthe wormhole, opening the possibility of using real samples of the carbon\nmaterial as a playground to experiment with the interaction between the\nbackground curvature and the Dirac fields.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ab initio study of structural stability of small 3$d$ late transition\n  metal clusters : Interplay of magnetization and hybridization: Using first-principles density functional theory based calculations, we\nanalyze the structural stability of small clusters of 3$d$ late transition\nmetals. We consider the relative stability of the two structures - layer-like\nstructure with hexagonal closed packed stacking and more compact structure of\nicosahedral symmetry. We find that the Co clusters show an unusual stability in\nhexagonal symmetry compared to the small clusters of other members which are\nfound to stabilize in icosahedral symmetry based structure. Our study reveals\nthat this is driven by the interplay between the magnetic energy gain and the\ngain in covalency through $s$-$d$ hybridization effect. Although we have\nfocused our study primarily on clusters of size 19 atoms, we find that this\nbehavior to be general for clusters having sizes between 15 and 20.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A Mechanical Implementation and Diagrammatic Calculation of Entangled\n  Basis States: We give for the first time a diagrammatic calculational tool of quantum\nentanglement. We present a pedagogical and simple mechanical implementation of\nquantum entanglement or \"spooky action at a distance\" to give a tangible\nrealization of this weird quantum mechanical concept alien to classical\nphysics. When two or more particles are correlated in a certain way, no matter\nhow far apart they are in space, their states remain correlated. Their\ncorrelation, which is instantaneous, does not seem to involve any communication\nwhich is limited by the speed of light. The same mechanical implementation\ndemonstrates the fundamental physical limits of any computational processes.\nThe analytical derivations of calculational entangled basis states are given\nand their corresponding diagrammatic representations give an efficient aid in\ndetermining the calculational entangled basis states. A quantum Fourier\ntransform for the two-state diagrams representing entangled basis states\n('renormalized qubits') can also be formulated. Our results seem to advocate\nthe idea that quantum entanglement generates the extra dimensions of the\ngravitational theory, indeed quantum entanglement is related to deep issues in\nthe unification of general relativity and quantum mechanics. This extra\ndimensions of spacetime entanglement are currently being speculated in the\nliterature.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "\"Reservoir model\" for shallow modulation-doped digital magnetic quantum\n  wells: Digital Magnetic Heterostructures (DMH) are semiconductor structures with\nmagnetic monolayers. Here we study electronic and magneto-transport properties\nof shallow modulation-doped (ZnSe/ZnCdSe) DMHs with spin-5/2 Mn impurities. We\ncompare the \"reservoir\" model, possibly relevant to shallow geometries, to the\nusual \"constant-density\" model. Our results are obtained by solving the\nKohn-Sham equations within the Local Spin Density Approximation (LSDA). In the\npresence of a magnetic field, we show that both models exhibit characteristic\nbehaviors for the electronic structure, two-dimensional carrier density, Fermi\nlevel and transport properties. Our results illustrate the relevance of\nexchange and correlation effects in the study shallow heterostructures of the\ngroup II-VI.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Analysis of the exciton-exciton interaction in semiconductor quantum\n  wells: The exciton-exciton interaction is investigated for quasi-two-dimensional\nquantum structures. A bosonization scheme is applied including the full spin\nstructure. For generating the effective interaction potentials, the\nHartree-Fock and Heitler-London approaches are improved by a full two-exciton\ncalculation which includes the van der Waals effect. With these potentials the\nbiexciton formation in bilayer systems is investigated. For coupled quantum\nwells the two-body scattering matrix is calculated and employed to give a\nmodified relation between exciton density and blue shift. Such a relation is of\ncentral importance for gauging exciton densities in experiments which pave the\nway toward Bose-Einstein condensation of excitons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Probing surface states exposed by crystal terminations at arbitrary\n  orientations of three-dimensional topological insulators: The topological properties of the bulk band structure of a three-dimensional\ntopological insulator (TI) manifest themselves in the form of metallic surface\nstates. In this paper, we propose a probe which directly couples to an exotic\nproperty of these surface states, namely the spin-momentum locking. We show\nthat the information regarding the spin textures, so extracted, for different\nsurfaces can be put together to reconstruct the parameters characterizing the\nbulk band structure of the material, hence acting as a hologram. For specific\nTI materials like, $\\text{Bi}_2\\text{Se}_3, \\text{Bi}_2\\text{Te}_3 \\text{and\nSb}_2\\text{Te}_3$, the planar surface states are distinct from one another with\nregard to their spectrum and the associated spin texture for each angle\n($\\theta$), which the normal to the surface makes with the crystal growth axis.\nWe develop a tunnel Hamiltonian between such arbitrary surfaces and a spin\npolarized STM which provides a unique fingerprint of the dispersion and the\nassociated spin texture corresponding to each $\\theta$. Additionally, the\ntheory presented in this article can be used to extract value of $\\theta$ for a\ngiven arbitrary planar surface from the STM spectra itself hence effectively\nmimicking X-ray spectroscopy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Contamination of polymethylmethacrylate by organic quantum emitters: We report the observation of ubiquitous contamination of\npolymethylmethacrylate by organic molecules with optical activity in the\nvisible spectral range. Contamination sites of individual solvent-specific\nfluorophores in thin films of polymethylmethacrylate constitute fluorescence\nhot-spots with quantum emission statistics and quantum yields approaching 30%\nat cryogenic temperatures. Our findings not only resolve prevalent puzzles in\nthe assignment of spectral features to various nanoemitters in polymer\nmatrices, they also identify means for simple and cost-efficient realization of\nsingle-photon sources in the visible spectral range.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effect of electron-phonon scattering on shot noise in nanoscale\n  junctions: We investigate the effect of electron-phonon inelastic scattering on shot\nnoise in nanoscale junctions in the regime of quasi-ballistic transport. We\npredict that when the local temperature of the junction is larger than its\nlowest vibrational mode energy $eV_c$, the inelastic contribution to shot noise\n(conductance) increases (decreases) with bias as $V$ ($\\sqrt{V}$). The\ncorresponding Fano factor thus increases as $\\sqrt{V}$. We also show that the\ninelastic contribution to the Fano factor saturates with increasing thermal\ncurrent exchanged between the junction and the bulk electrodes to a value\nwhich, for $V>>V_c$, is independent of bias. A measurement of shot noise may\nthus provide information about the local temperature and heat dissipation in\nnanoscale conductors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum heat transfer: A Born Oppenheimer method: We develop a Born-Oppenheimer type formalism for the description of quantum\nthermal transport along hybrid nanoscale objects. Our formalism is suitable for\ntreating heat transfer in the off-resonant regime, where e.g., the relevant\nvibrational modes of the interlocated molecule are high relative to typical\nbath frequencies, and at low temperatures when tunneling effects dominate. A\ngeneral expression for the thermal energy current is accomplished, in the form\nof a generalized Landauer formula. In the harmonic limit this expression\nreduces to the standard Landauer result for heat transfer, while in the\npresence of nonlinearities multiphonon tunneling effects are realized.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological Wannier cycles for the bulk and edges: Topological materials are often characterized by unique edge states which are\nin turn used to detect different topological phases in experiments. Recently,\nwith the discovery of various higher-order topological insulators, such\nspectral topological characteristics are extended from edge states to corner\nstates. However, the chiral symmetry protecting the corner states is often\nbroken in genuine materials, leading to vulnerable corner states even when the\nhigher-order topological numbers remain quantized and invariant. Here, we show\nthat a local artificial gauge flux can serve as a robust probe of the Wannier\ntype higher-order topological insulators which is effective even when the\nchiral symmetry is broken. The resultant observable signature is the emergence\nof the cyclic spectral flows traversing one or multiple band gaps. These\nspectral flows are associated with the local modes bound to the artificial\ngauge flux. This phenomenon is essentially due to the cyclic transformation of\nthe Wannier orbitals when the local gauge flux acts on them. We extend\ntopological Wannier cycles to systems with C2 and C3 symmetries and show that\nthey can probe both the bulk and the edge Wannier centers, yielding rich\ntopological phenomena.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Relation between unidirectional spin Hall magnetoresistance and spin\n  current-driven magnon generation: We perform electronic measurements of unidirectional spin Hall\nmagnetoresistance (USMR) in a Permalloy/Pt bilayer, in conjunction with\nmagneto-optical Brillouin light spectroscopy of spin current-driven magnon\npopulation. We show that the current dependence of USMR closely follows the\ndipolar magnon density, and that both dependencies exhibit the same scaling\nover a large temperature range of 80-400 K. These findings demonstrate a close\nrelationship between spin current-driven magnon generation and USMR, and\nindicate that the latter is likely dominated by the dipolar magnons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fano-Josephson effect of Majorana bound states: We investigate the Josephson current in a Fano-Josephson junction formed by\nthe direct coupling between two topological superconducting wires and their\nindirect coupling via a quantum dot. It is found that when two Majorana zero\nmodes respectively appear in the wires, the Fano interference causes abundant\nJosephson phase transition processes. What is notable is that in the presence\nof appropriate direct and indirect inter-wire couplings, the fractional\nJosephson effect disappears and then such a structure transforms into a\n$0$-phase normal Josephson junction. On the other hand, if finite coupling\noccurs between the Majorana bound states at the ends of each wire, the normal\nJosepshon current is robustly in the $0$ phase, weakly dependent on the Fano\neffect. We believe that the results in this work are helpful for describing the\nFano-modified Josephson effect.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Steady-State Entanglement in the Nuclear Spin Dynamics of a Double\n  Quantum Dot: We propose a scheme for the deterministic generation of steady-state\nentanglement between the two nuclear spin ensembles in an electrically defined\ndouble quantum dot. Due to quantum interference in the collective coupling to\nthe electronic degrees of freedom, the nuclear system is actively driven into a\ntwo-mode squeezed-like target state. The entanglement build-up is accompanied\nby a self-polarization of the nuclear spins towards large Overhauser field\ngradients. Moreover, the feedback between the electronic and nuclear dynamics\nleads to multi-stability and criticality in the steady-state solutions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Modulating spin relaxation in nanowires with infrared light at room\n  temperature: Spintronic devices usually rely on long spin relaxation times and/or lengths\nfor optimum performance. Therefore, the ability to modulate these quantities\nwith an external agent offers unique possibilities. The dominant spin\nrelaxation mechanism in most technologically important semiconductors is the\nD'yakonov-Perel' (DP) mechanism which vanishes if the spin carriers (electrons)\nare confined to a single conduction subband in a quantum wire grown in certain\ncrystallographic directions, or polycrystalline quantum wires. Here, we report\nmodulating the DP spin relaxation rate (and hence the spin relaxation length)\nin self assembled 50-nm diameter InSb nanowires with infrared light at room\ntemperature. In the dark, almost all the electrons in the nanowires are in the\nlowest conduction subband at room temperature, resulting in near-complete\nabsence of DP relaxation. This allows observation of spin-sensitive effects in\nthe magnetoresistance. Under infrared illumination, electrons are photoexcited\nto higher subbands and the DP spin relaxation mechanism is revived, leading to\na three-fold decrease in the spin relaxation length. Consequently, the spin\nsensitive effects are no longer observable under illumination. This phenomenon\nmay have applications in spintronic room-temperature infrared photodetection.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermally-Assisted Spin-Transfer Torque Magnetization Reversal of\n  Uniaxial Nanomagnets in Energy Space: The asymptotic behavior of switching time as a function of current for a\nuniaxial macrospin under the effects of both spin-torque and thermal noise is\nexplored analytically by focusing on its diffusive energy space dynamics. The\nscaling dependence ($I\\rightarrow 0$, $<\\tau\\propto\\exp(-\\xi(1-I)^2)$) is shown\nto confirm recent literature results. The analysis shows the mean switching\ntime to be functionally independent of the angle between the spin current and\nmagnet's uniaxial axes. These results have important implications for modeling\nthe energetics of thermally assisted magnetization reversal of spin transfer\nmagnetic random access memory bit cells.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Chirality from interfacial spin-orbit coupling effects in magnetic\n  bilayers: As nanomagnetic devices scale to smaller sizes, spin-orbit coupling due to\nthe broken structural inversion symmetry at interfaces becomes increasingly\nimportant. Here we study interfacial spin-orbit coupling effects in magnetic\nbilayers using a simple Rashba model. The spin-orbit coupling introduces\nchirality into the behavior of the electrons and through them into the\nenergetics of the magnetization. In the derived form of the magnetization\ndynamics, all of the contributions that are linear in the spin-orbit coupling\nfollow from this chirality, considerably simplifying the analysis. For these\nsystems, an important consequence is a correlation between the\nDzyaloshinskii-Moriya interaction and the spin-orbit torque. We use this\ncorrelation to analyze recent experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Excitons in atomically thin black phosphorus: Raman scattering and photoluminescence spectroscopy are used to investigate\nthe optical properties of single layer black phosphorus obtained by mechanical\nexfoliation of bulk crystals under an argon atmosphere. The Raman spectroscopy,\nperformed in situ on the same flake as the photoluminescence measurements,\ndemonstrates the single layer character of the investigated samples. The\nemission spectra, dominated by excitonic effects, display the expected in plane\nanisotropy. The emission energy depends on the type of substrate on which the\nflake is placed due to the different dielectric screening. Finally, the blue\nshift of the emission with increasing temperature is well described using a two\noscillator model for the temperature dependence of the band gap.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Towards Substrate Engineering of Graphene-Silicon Schottky Diode\n  Photodetectors: Graphene-Silicon Schottky diode photodetectors possess beneficial properties\nsuch as high responsivities and detectivities, broad spectral wavelength\noperation and high operating speeds. Various routes and architectures have been\nemployed in the past to fabricate devices. Devices are commonly based on the\nremoval of the silicon-oxide layer on the surface of silicon by wet-etching\nbefore deposition of graphene on top of silicon to form the graphene-silicon\nSchottky junction. In this work, we systematically investigate the influence of\nthe interfacial oxide layer, the fabrication technique employed and the silicon\nsubstrate on the light detection capabilities of graphene-silicon Schottky\ndiode photodetectors. The properties of devices are investigated over a broad\nwavelength range from near-UV to short-/mid-infrared radiation, radiation\nintensities covering over five orders of magnitude as well as the suitability\nof devices for high speed operation. Results show that the interfacial layer,\ndepending on the required application, is in fact beneficial to enhance the\nphotodetection properties of such devices. Further, we demonstrate the\ninfluence of the silicon substrate on the spectral response and operating\nspeed. Fabricated devices operate over a broad spectral wavelength range from\nthe near-UV to the short-/mid-infrared (thermal) wavelength regime, exhibit\nhigh photovoltage responses approaching 10$^6$ V/W and short rise- and\nfall-times of tens of nanoseconds.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interference Effects on Kondo-Assisted Transport through Double Quantum\n  Dots: We systematically investigate electron transport through double quantum dots\nwith particular emphasis on interference induced via multiple paths of electron\npropagation. By means of the slave-boson mean-field approximation, we calculate\nthe conductance, the local density of states, the transmission probability in\nthe Kondo regime at zero temperature. It is clarified how the Kondo-assisted\ntransport changes its properties when the system is continuously changed among\nthe serial, parallel and T-shaped double dots. The obtained results for the\nconductance are explained in terms of the Kondo resonances influenced by\ninterference effects. We also discuss the impacts due to the spin-polarization\nof ferromagnetic leads.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum transport through single and multilayer icosahedral fullerenes: We use a tight-binding Hamiltonian and Green functions methods to calculate\nthe quantum transmission through single-wall fullerenes and bilayered and\ntrilayered onions of icosahedral symmetry attached to metallic leads. The\nelectronic structure of the onion-like fullerenes takes into account the\ncurvature and finite size of the fullerenes layers as well as the strength of\nthe intershell interactions depending on to the number of interacting atom\npairs belonging to adjacent shells. Misalignment of the symmetry axes of the\nconcentric icosahedral shells produces breaking of the level degeneracies of\nthe individual shells, giving rise some narrow quasi-continuum bands instead of\nthe localized discrete peaks of the individual fullerenes. As a result, the\ntransmission function for non symmetrical onions are rapidly varying functions\nof the Fermi energy. Furthermore, we found that most of the features of the\ntransmission through the onions are due to the electronic structure of the\nouter shell with additional Fano-like antiresonances arising from coupling with\nor between the inner shells.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Low conductance of the nickel atomic junctions in hydrogen atmosphere: The low conductance of nickel atomic junctions in the hydrogen environment is\nstudied using the nonequilibrium Green's function theory combined with\nfirst-principles calculations. The Ni junction bridged by a $H_2$ molecule has\na conductance of approximately 0.7 $G_0$. This conductance is contributed by\nthe anti-bonding state of the $H_2$ molecule, which forms a bonding state with\nthe $3d$ orbitals of the nearby Ni atoms. In contrast, the Ni junction bridged\nby the two single H atoms has a conductance of approximately 1 $G_0$, which is\nweakly spin-polarized. The spin-up channels were found to contribute mostly to\nthe conductance at a small junction gap, while the spin-down channels play a\ndominant role at a larger junction gap.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A scattering model of 1D quantum wire regular polygons: We calculate the quantum states of regular polygons made of 1D quantum wires\ntreating each polygon vertex as a scatterer. The vertex scattering matrix is\nanalytically obtained from the model of a circular bend of a given angle of a\n2D nanowire. In the single mode limit the spectrum is classified in doublets of\nvanishing circulation, twofold split by the small vertex reflection, and\nsinglets with circulation degeneracy. Simple analytic expressions of the energy\neigenvalues are given. It is shown how each polygon is characterized by a\nspecific spectrum.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Controlling transport properties of graphene nanoribbons by\n  codoping-induced edge distortions: One notable manifestation of the peculiar edge-localized states in zigzag\ngraphene nanoribbons (zGNRs) is the p-type (n-type) characteristics of nitrogen\n(boron) edge-doped GNRs, and such behavior was so far considered to be\nexclusive for zGNRs. Carrying out first-principles electronic structure and\nquantum transport calculations, we herein show that the donor-acceptor\ntransition behavior can also arise in the B/N edge-doped armchair GNRs (aGNRs)\nby introducing a bipolar P codopant atom into the energetically most favorable\nnearest neighbor edge sites. The n-type (p-type) transport properties of B,P\n(N,P) co-doped aGNRs are also shown to be superior to those of reference single\nN (B) doped aGNRs in that the valence (conduction) band edge conductance\nspectra are better preserved. Disentangling the chemical doping and structural\ndistortion effects, we will demonstrate that the latter plays an important role\nin determining the transport type and explains the donor-acceptor transition\nfeature as well as the bipolar character of P-doped aGNRs. We thus propose the\nsystematic modification of GNR edge atomic structures via co-doping as a novel\napproach to control charge transport characteristics of aGNRs.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current-induced mechanical torque in chiral molecular rotors: A great endeavor has been undertaken to engineer molecular rotors operated by\nan electrical current. A frequently met operation principle is the transfer of\nangular momentum taken from the incident flux. In this paper we present an\nalternative driving agent that works also in situations where angular momentum\nof the incoming flux is conserved. This situation arises typically with\nmolecular rotors that exhibit an easy axis of rotation. For quantitative\nanalysis we investigate here a classical model, where molecule and wires are\nrepresented by a rigid curved path. We demonstrate that in the presence of\nchirality the rotor generically undergoes a directed motion, provided that the\nincident current exceeds a threshold value. Above threshold, the corresponding\nrotation frequency (per incoming particle current) for helical geometries turns\nout to be $2\\pi m/M_1$, where $m/M_1$ is the ratio of the mass of an incident\ncharge carrier and the mass of the helix per winding number.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Low-power photothermal self-oscillation of bimetallic nanowires: We investigate the nonlinear mechanics of a bimetallic, optically absorbing\nSiN-Nb nanowire in the presence of incident laser light and a reflecting Si\nmirror. Situated in a standing wave of optical intensity and subject to\nphotothermal forces, the nanowire undergoes self-induced oscillations at low\nincident light thresholds of $<1\\, \\rm{\\mu W}$ due to engineered strong\ntemperature-position ($T$-$z$) coupling. Along with inducing self-oscillation,\nlaser light causes large changes to the mechanical resonant frequency\n$\\omega_0$ and equilibrium position $z_0$ that cannot be neglected. We present\nexperimental results and a theoretical model for the motion under laser\nillumination. In the model, we solve the governing nonlinear differential\nequations by perturbative means to show that self-oscillation amplitude is set\nby the competing effects of direct $T$-$z$ coupling and $2\\omega_0$ parametric\nexcitation due to $T$-$\\omega_0$ coupling. We then study the linearized\nequations of motion to show that the optimal thermal time constant $\\tau$ for\nphotothermal feedback is $\\tau \\to \\infty$ rather than the widely reported\n$\\omega_0 \\tau = 1$. Lastly, we demonstrate photothermal quality factor ($Q$)\nenhancement of driven motion as a means to counteract air damping.\nUnderstanding photothermal effects on micromechanical devices, as well as\nnonlinear aspects of optics-based motion detection, can enable new device\napplications as oscillators or other electronic elements with smaller device\nfootprints and less stringent ambient vacuum requirements.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-Hermitian Boundary Modes: We consider conditions for the existence of boundary modes in non-Hermitian\nsystems with edges of arbitrary co-dimension. Through a universal formulation\nof formation criteria for boundary modes in terms of local Green functions, we\noutline a generic perspective on the appearance of such modes and generate\ncorresponding dispersion relations. In the process, we explain the skin effect\nin both topological and non-topological systems, exhaustively generalizing\nbulk-boundary correspondence in the presence of non-Hermiticity. This is\naccomplished via a doubled Green's function, inspired by doubled Hamiltonian\nmethods used to classify Floquet and, more recently, non-Hermitian topological\nphases. Our work constitutes a general tool, as well as, a unifying perspective\nfor this rapidly evolving field. Indeed, as a concrete application we find that\nour method can expose novel non-Hermitian topological regimes beyond the reach\nof previous methods.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fast and anomalous exciton diffusion in two-dimensional hybrid\n  perovskites: Two-dimensional hybrid perovskites are currently in the spotlight of\ncondensed matter and nanotechnology research due to their intriguing\noptoelectronic and vibrational properties with emerging potential for\nlight-harvesting and -emitting applications. While it is known that these\nnatural quantum wells host tightly bound excitons, the mobilities of these\nfundamental optical excitations at the heart of the optoelectronic applications\nare still largely unexplored. Here, we directly monitor the diffusion of\nexcitons through ultrafast emission microscopy from liquid helium to room\ntemperature in hBN-encapsulated two-dimensional hybrid perovskites. We find\nvery fast diffusion with characteristic hallmarks of free exciton propagation\nfor all temperatures above 50 K. In the cryogenic regime we observe nonlinear,\nanomalous behavior with an exceptionally rapid expansion of the exciton cloud\nfollowed by a very slow and even negative effective diffusion. We discuss our\nfindings in view of efficient exciton-phonon coupling, highlighting\ntwo-dimensional hybrids as promising platforms for many-body physics research\nand optoelectronic applications on the nanoscale.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Delocalisation of Majorana quasiparticles in plaquette--nanowire hybrid\n  system: Interplay between superconductivity, spin-orbit coupling and magnetic field\ncan lead to realisation of the topologically non--trivial states which in\nfinite one dimensional nanowires are manifested by emergence of a pair of\nzero-energy Majorana bound states. On the other hand, in two dimensional\nsystems spin current contributed by the edge states might appear. We\ninvestigate novel properties of the bound states in a system of mixed\ndimensionality, composed of one-dimensional nanowire connected with\ntwo-dimensional plaquette. This setup could be patterned epitaxially, e.g.\nusing heterostructure analogous to what has been reported recently by F.\nNichele et al., Phys. Rev. Lett. 119, 136803 (2017). We study this system,\nassuming either its part or the entire structure to be in topologically\nnon--trivial superconducting state. Our results predict delocalisation of the\nMajorana modes, upon leaking from the nanowire to the nanocluster with some\ntendency towards its corners.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Waiting time distributions in Quantum spin hall based heterostructures: For the distinction of the Andreev bound states and Majorana bound states, we\nstudy the waiting time distributions (WTDs) for heterostructures, based on one\ndimensional edge states of a two dimensional topological insulators (TI) in\ncombination with an proximitized s-wave superconductor (SC) and an applied\nmagnetic field. We show for the time reversal symmetric (TRS) situation of a\nJosephson junction details of the WTD. This includes different transport\nprocesses, different numbers of Andreev bound states and the phase difference\nof the SC. We further consider a Zeeman field in the normal part of the\njunctions revealing novel features in the WTD along the phase transition\nbetween trivial bound states and Majorana bound states. We finally discuss\nclear signatures to discriminate between them.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "High-speed metamagnetic resistive switching of FeRh through Joule\n  heating: Due to its proximity to room temperature and demonstrated high degree of\ntemperature tunability, the metamagnetic ordering transition in FeRh is\nattractive for novel high-performance computing devices seeking to use\nmagnetism as the state variable. We demonstrate electrical control of the\ntransition via Joule heating in FeRh wires. Finite element simulations based on\nabrupt state transition within each domain result in a globally smooth\ntransition that agrees with the experimental findings and provides insight into\nthe thermodynamics involved. We measure a 150 K decrease in transition\ntemperature with currents up to 60 mA, limited only by the dimensions of the\ndevice. The sizeable shift in transition temperature scales with current\ndensity and wire length, suggesting the absolute resistance and heat\ndissipation of the substrate are also important. The FeRh phase change is\nevaluated by pulsed I-V using a variety of bias conditions. We demonstrate high\nspeed (~ ns) memristor-like behavior and report device performance parameters\nsuch as switching speed and power consumption that compare favorably with\nstate-of-the-art phase change memristive technologies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Contact-induced negative differential resistance in short-channel\n  graphene FETs: In this work, we clarify the physical mechanism for the phenomenon of\nnegative output differential resistance (NDR) in short-channel graphene FETs\n(GFETs) through non-equilibrium Green's function (NEGF) simulations and a\nsimpler semianalytical ballistic model that captures the essential physics.\nThis NDR phenomenon is due to a transport mode bottleneck effect induced by the\ngraphene Dirac point in the different device regions, including the contacts.\nNDR is found to occur only when the gate biasing produces an n-p-n or p-n-p\npolarity configuration along the channel, for both positive and negative\ndrain-source voltage sweep. In addition, we also explore the impact on the NDR\neffect of contact-induced energy broadening in the source and drain regions and\na finite contact resistance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Control of a spin qubit in a lateral GaAs quantum dot based on symmetry\n  of gating potential: We study the influence of quantum dot symmetry on the Rabi frequency and\nphonon induced spin relaxation rate in a single electron GaAs spin qubit. We\nfind that anisotropic dependence on the magnetic field direction is independent\nof the choice of the gating potential. Also, we discover that relative\norientation of the quantum dot, with respect to the crystallographic frame, is\nrelevant in systems with ${\\bf C}_{1{\\rm v}}$, ${\\bf C}_{2{\\rm v}}$, or ${\\bf\nC}_{n}$ ($n\\neq4r$) symmetry. To demonstrate the important impact of the gating\npotential shape on the spin qubit lifetime, we compare the effects of an\nequilateral triangle, square, and rectangular confinement with the known\nresults for the harmonic potential. In the studied cases, enhanced spin qubit\nlifetime is revealed, reaching almost six orders of magnitude increase for the\nequilateral triangle gating.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coherent radiation by magnets with exchange interactions: A wide class of materials acquires magnetic properties due to particle\ninteractions through exchange forces. These can be atoms and molecules\ncomposing the system itself, as in the case of numerous magnetic substances. Or\nthese could be different defects, as in the case of graphene, graphite, carbon\nnanotubes, and related materials. The theory is suggested describing fast\nmagnetization reversal in magnetic systems, whose magnetism is caused by\nexchange interactions. The effect is based on the coupling of a magnetic sample\nwith an electric circuit producing a feedback magnetic field. This method can\nfind various applications in spintronics. The magnetization reversal can be\nself-organized, producing spin superradiance. A part of radiation is absorbed\nby a resonator magnetic coil. But an essential part of radiation can also be\nemitted through the coil sides.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Second-order polaron resonances in self assembled quantum dots: We theoretically study the optical properties of an InAs/GaAs quantum dot\n(QD) near the area of the second-order resonance between an electron confined\nin the QD and two longitudinal optical phonons. We present the absorption\nspectra of an inhomogeneously broadened QD ensemble and show that the minimal\nmodel needed for an accurate description of such a system needs to account for\n3-phonon states. We study also the influence of the QD height to width ratio on\nthe optical properties of the polaron system. The dependence of the width of\nthe resonance and the position of the second-order resonant feature on the\nheight to width ratio is presented.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Polarization Of Quantum Hall States, Skyrmions and Berry Phase: We have discussed here the polarization of quantum Hall states in the\nframework of the hierarchical analysis of IQHE and FQHE in terms of Berry\nphase. It is observed that we have fully polarized states for the filling\nfactor $\\nu=1$ as well as $\\nu=\\frac{1}{2m+1}$, $m$ being an integer. However,\nfor $\\nu=p$ as well as $\\nu =\\frac{p}{q}$, with $p>1$ and odd, $q$ odd we have\npartially polarized states and for $\\nu=\\frac{p}{q}$, $p$ even, $q$ odd we have\nunpolarized states. It has been found that skyrmion excitations exist only for\nfully polarized states and for partially polarized and unpolarized states\nskyrmionic excitations do not exist.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetization dynamics and spin pumping induced by standing elastic\n  waves: The magnetization dynamics induced by standing elastic waves excited in a\nthin ferromagnetic film is described with the aid of micromagnetic simulations\ntaking into account the magnetoelastic coupling between spins and lattice\nstrains. The simulations have been performed for the 2 nm thick Fe81Ga19 film\ndynamically strained by longitudinal and transverse standing waves with various\nfrequencies, which span a wide range around the resonance frequency nu_res of\ncoherent magnetization precession in unstrained Fe81Ga19 film. It is found that\nstanding elastic waves give rise to complex local magnetization dynamics and\nspatially inhomogeneous dynamic magnetic patterns. The spatio-temporal\ndistributions of the magnetization oscillations in standing elastic waves have\nthe form of standing spin waves with the same wavelength. Remarkably, the\namplitude of magnetization precession does not go to zero at the nodes of these\nspin waves, which cannot be precisely described by simple analytical formulae.\nIn the steady-state regime, the magnetization oscillates with the frequency of\nelastic wave, except for the case of longitudinal waves with frequencies well\nbelow nu_res, where the magnetization precesses with a variable frequency\nstrongly exceeding the wave frequency. The precession amplitude at the\nantinodes of standing spin waves strongly increases when the frequency of\nelastic wave becomes close to nu_res. The results obtained for the\nmagnetization dynamics driven by elastic waves are used to calculate the spin\ncurrent pumped from the dynamically strained ferromagnet into adjacent\nparamagnetic metal. Importantly, the transverse charge current created by the\nspin current via the inverse spin Hall effect is high enough to be measured\nexperimentally.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic anisotropy in surface-supported single-ion lanthanide complexes: Single-ion lanthanide-organic complexes can provide stable magnetic moments\nwith well-defined orientation for spintronic applications on the atomic level.\nHere, we show by a combined experimental approach of scanning tunneling\nmicroscopy and X-ray absorption spectroscopy that\ndysprosium-tris(1,1,1-trifluoro-4-(2-thienyl)-2,4butanedionate) (Dy(tta)$_3$)\ncomplexes deposited on a Au(111) surface undergo a molecular distortion,\nresulting in distinct crystal field symmetry imposed on the Dy ion. This leads\nto an easy-axis magnetization direction in the ligand plane. Furthermore, we\nshow that tunneling electrons hardly couple to the spin excitations, which we\nascribe to the shielded nature of the $4f$ electrons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Light-Driven Nanoscale Vectorial Currents: Controlled charge flows are fundamental to many areas of science and\ntechnology, serving as carriers of energy and information, as probes of\nmaterial properties and dynamics, and as a means of revealing or even inducing\nbroken symmetries. Emerging methods for light-based current control offer\npromising routes beyond the speed and adaptability limitations of conventional\nvoltage-driven systems. However, optical generation and manipulation of\ncurrents at nanometer spatial scales remains a basic challenge and a crucial\nstep towards scalable optoelectronic systems for microelectronics and\ninformation science. Here, we introduce vectorial optoelectronic metasurfaces\nin which ultrafast light pulses induce local directional charge flows around\nsymmetry-broken plasmonic nanostructures, with tunable responses and arbitrary\npatterning down to sub-diffractive nanometer scales. Local symmetries and\nvectorial current distributions are revealed by polarization- and\nwavelength-sensitive electrical readout and terahertz (THz) emission, while\nspatially-tailored global currents are demonstrated in the direct generation of\nelusive broadband THz vector beams. We show that in graphene, a detailed\ninterplay between electrodynamic, thermodynamic, and hydrodynamic degrees of\nfreedom gives rise to rapidly-evolving nanoscale driving forces and charge\nflows under extreme temporal and spatial confinement. These results set the\nstage for versatile patterning and optical control over nanoscale currents in\nmaterials diagnostics, THz spectroscopies, nano-magnetism, and ultrafast\ninformation processing.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Surface Percolation and Growth. An alternative scheme for breaking the\n  diffraction limit in optical patterning: A nanopatterning scheme is presented by which the structure height can be\ncontrolled in the tens of nanometers range and the lateral resolution is a\nfactor at least three times better than the point spread function of the\nwriting beam. The method relies on the initiation of the polymerization\nmediated by a very inefficient energy transfer from a fluorescent dye molecule\nafter single photon absorption. The mechanism has the following distinctive\nsteps: the dye adsorbs on the substrate surface with a higher concentration\nthan in the bulk, upon illumination it triggers the polymerization, then\nisolated islands develop and merge into a uniform structure (percolation),\nwhich subsequently grows until the illumination is interrupted. This\npercolation mechanism has a threshold that introduces the needed nonlinearity\nfor the fabrication of structures beyond the diffraction limit.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron-Hole Liquid in Monolayer Transition Metal Dichalcogenide\n  Heterostructures: Monolayer films of transition metal dichalcogenides (in particular, MoS2,\nMoSe2, WS2, and WSe2) can be considered as ideal systems for the studies of\nhigh-temperature electron-hole liquids. The quasi-two-dimensional nature of\nelectrons and holes ensures their stronger interaction as compared to that in\nbulk semiconductors. The screening of the Coulomb interaction in monolayer\nheterostructures is significantly reduced, since it is determined by the\npermittivities of the environment (e.g., vacuum and substrate), which are much\nlower than those characteristic of the films of transition metal\ndichalcogenides. The multivalley structure of the energy spectrum of charge\ncarriers in transition metal dichalcogenides significantly reduces the kinetic\nenergy, resulting in the increase in the equilibrium density and binding energy\nof the electron-hole liquid. The binding energy of the electron-hole liquid and\nits equilibrium density are determined. It is shown that the two-dimensional\nCoulomb potential should be used in the calculations for the electron-hole\nliquid.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The specific heat and the radial thermal expansion of bundles of\n  single-walled carbon nanotubes: The specific heat at constant pressure of bundles of single-walled carbon\nnanotubes closed at their ends has been investigated in a temperature interval\nof 2-120 K. It is found that the curve of heat capacity has features near 5,\n36, 80, and 100 K. The experimental results on the heat capacity and the radial\nthermal expansion coefficient of bundles of SWNTs oriented perpendicular to the\nsample axis have been compared. It is found that the curves of the heat\ncapacity and the radial thermal expansion coefficient exhibit a similar\ntemperature behavior above 10 K. The temperature dependence of the Gruneisen\ncoefficient has been calculated. The curve of the Gruneisen coefficient also\nhas a feature near 36 K. Above 36 K the Gruneisen coefficient is practically\nindependent of temperature. Below 36 K the Gruneisen coefficient decreases\nmonotonically with lowering temperature and becomes negative below 6 K.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical orientation of excitons in a longitudinal magnetic field in\n  indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment: The exciton recombination and spin dynamics in (In,Al)As/AlAs quantum dots\n(QDs) with indirect band gap and type-I band alignment are studied. The\nnegligible (less than $0.2~\\mu$eV) value of the anisotropic exchange\ninteraction in these QDs prevents a mixing of the excitonic basis states with\npure spin and allows for the formation of spin polarized bright excitons for\nquasi-resonant circularly polarized excitation. In a longitudinal magnetic\nfield, the recombination and spin dynamics of the excitons are controlled by\nthe hyperfine interaction between the electron and nuclear spins. A QD blockade\nby dark excitons is observed in magnetic field eliminating the impact of the\nnuclear spin fluctuations. A kinetic equation model, which accounts for the\npopulation dynamics of the bright and dark exciton states as well as for the\nspin dynamics, has been developed, which allows for a quantitative description\nof the experimental data.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spectral and transport properties of the two-dimensional Lieb lattice: The specific topology of the line centered square lattice (known also as the\nLieb lattice) induces remarkable spectral properties as the macroscopically\ndegenerated zero energy flat band, the Dirac cone in the low energy spectrum,\nand the peculiar Hofstadter-type spectrum in magnetic field. We study here the\nproperties of the finite Lieb lattice with periodic and vanishing boundary\nconditions. We find out the behavior of the flat band induced by disorder and\nexternal magnetic and electric fields. We show that in the confined Lieb\nplaquette threaded by a perpendicular magnetic flux there are edge states with\nnontrivial behavior. The specific class of twisted edge states, which have\nalternating chirality, are sensitive to disorder and do not support IQHE, but\ncontribute to the longitudinal resistance. The symmetry of the transmittance\nmatrix in the energy range where these states are located is revealed. The\ndiamagnetic moments of the bulk and edge states in the Dirac-Landau domain, and\nalso of the flat states in crossed magnetic and electric fields are shown.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Microwave amplification with nanomechanical resonators: Sensitive measurement of electrical signals is at the heart of modern science\nand technology. According to quantum mechanics, any detector or amplifier is\nrequired to add a certain amount of noise to the signal, equaling at best the\nenergy of quantum fluctuations. The quantum limit of added noise has nearly\nbeen reached with superconducting devices which take advantage of\nnonlinearities in Josephson junctions. Here, we introduce a new paradigm of\namplification of microwave signals with the help of a mechanical oscillator. By\nrelying on the radiation pressure force on a nanomechanical resonator, we\nprovide an experimental demonstration and an analytical description of how the\ninjection of microwaves induces coherent stimulated emission and signal\namplification. This scheme, based on two linear oscillators, has the advantage\nof being conceptually and practically simpler than the Josephson junction\ndevices, and, at the same time, has a high potential to reach quantum limited\noperation. With a measured signal amplification of 25 decibels and the addition\nof 20 quanta of noise, we anticipate near quantum-limited mechanical microwave\namplification is feasible in various applications involving integrated\nelectrical circuits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Second-Harmonic Generation in Nano-Structured Metamaterials: We conduct a theoretical and numerical study on the second-harmonic (SH)\noptical response of a nano-structured metamaterial composed of a periodic array\nof inclusions. Both the inclusions and their surrounding matrix are made of\ncentrosymmetrical materials, for which SH is strongly suppressed, but by\nappropriately choosing the shape of the inclusions, we may produce a\ngeometrically non-centrosymmetric system which does allow efficient SH\ngeneration. Variations in the geometrical configuration allows tuning the\nlinear and quadratic spectra of the optical response of the system. We develop\nan efficient scheme for calculating the nonlinear polarization, extending a\nformalism for the calculation of the macroscopic dielectric function using\nHaydock's recursion method. We apply the formalism developed here to an array\nof holes within an Ag matrix, but it can be readily applied to any metamaterial\nmade of arbitrary materials and for inclusions of any geometry within the\nlong-wavelength regime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Terahertz-induced resistance oscillations in high mobility\n  two-dimensional electron systems: We report on a theoretical work on magnetotransport under terahertz radiation\nwith high mobility two-dimensional electron systems. We focus on the\ninteraction between the obtained radiation-induced magnetoresistance\noscillations (RIRO) and the Shubnikov-de Haas (SdHO) oscillations. We study two\neffects experimentally obtained with this radiation. First, the observed\ndisappearance of the SdHO oscillations simultaneously with the vanishing\nresistance at the zero resistance states region. And secondly the strong\nmodulation of the SdHO oscillations at sufficient terahertz radiation power. We\nconclude that both effects share the same physical origin, the interference\nbetween the average advanced distance by the scattered electron between\nirradiated Landau states, (RIRO), and the available initial density of states\nat a certain magnetic field, (SdHO). Thus, from a physical standpoint, what the\nterahertz experiments and theoretical simulations reveal is, on the one hand,\nthe oscillating nature of the Landau states subjected to radiation and, on the\nother hand, how they behave in the presence of scattering.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Are Microwave Induced Zero Resistance States Necessarily Static?: We study the effect of inhomogeneities in Hall conductivity on the nature of\nthe Zero Resistance States seen in the microwave irradiated two-dimensional\nelectron systems in weak perpendicular magnetic fields, and we show that\ntime-dependent domain patterns may emerge in some situations. For an annular\nCorbino geometry, with an equilibrium charge density that varies linearly with\nradius, we find a time-periodic non-equilibrium solution, which might be\ndetected by a charge sensor, such as an SET. For a model on a torus, in\naddition to static domain patterns seen at high and low values of the\nequilibrium charge inhomogeneity, we find that, in the intermediate regime, a\nvariety of nonstationary states can also exist. We catalog the possibilities we\nhave seen in our simulations. Within a particular phenomenological model, we\nshow that linearizing the nonlinear charge continuity equation about a\nparticularly simple domain wall configuration and analyzing the eigenmodes\nallows us to estimate the periods of the solutions to the full nonlinear\nequation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Exchange interaction effects in the thermodynamic properties of quantum\n  dots: We study electron-electron interaction effects in the thermodynamic\nproperties of quantum-dot systems. We obtain the direct and exchange\ncontributions to the specific heat C_v in the self-consistent Hartree-Fock\napproximation at finite temperatures. An exchange-induced phase transition is\nobserved and the transition temperature is shown to be inversely proportional\nto the size of the system. The exchange contribution to C_v dominates over the\ndirect and kinetic contributions in the intermediate regime of interaction\nstrength (r_s ~ 1). Furthermore, the electron-electron interaction modifies\nboth the amplitude and the period of magnetic field induced oscillations in\nC_v.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Scattering by linear defects in graphene: a tight-binding approach: We develop an analytical scattering formalism for computing the transmittance\nthrough periodic defect lines within the tight-binding model of graphene. We\nfirst illustrate the method with a relatively simple case, the pentagon-only\ndefect line. Afterwards, more complex defect lines are treated, namely the\nzz(558) and the zz(5757) ones. The formalism developed, only uses simple\ntight-binding concepts, reducing the problem to matrix manipulations which can\nbe easily worked out by any computational algebraic calculator.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Screening of a Luttinger liquid wire by a scanning tunneling microscope\n  tip: II. Transport properties: We study the effect of an electrostatic coupling between a scanning tunneling\nmicroscope tip and a Luttinger liquid wire on the tunneling current and noise\nbetween the two. Solving the Dyson equations non perturbatively for a local\ninteraction potential, we derive the Green's functions associated to the wire\nand to the tip. Interestingly, the electrostatic coupling leads to the\nexistence of new correlators, which we call mixed Green's functions, which are\ncorrelators between the bosonic fields of the wire and the tip. Next, we\ncalculate the transport properties up to second order with the amplitude of the\ntunnel transfer: the tunnel current is strongly reduced by the presence of\nscreening. The zero-frequency noise is modified in a similar way, but the Fano\nfactor remains unchanged. We also consider the effect of the screening on the\nasymmetry of the finite-frequency non-symmetrized noise and on the conductance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Oxygen vacancies dynamics in redox-based interfaces: Tailoring the\n  memristive response: Redox-based memristive devices are among the alternatives for the next\ngeneration of non volatile memories, but also candidates to emulate the\nbehavior of synapses in neuromorphic computing devices. It is nowadays well\nestablished that the motion of oxygen vacancies (OV) at the nanoscale is the\nkey mechanism to reversibly switch metal/insulator/metal structures from\ninsulating to conducting, i.e. to accomplish the resistive switching effect.\nThe control of OV dynamics has a direct effect on the resistance changes, and\ntherefore on different figures of memristive devices, such as switching speed,\nretention, endurance or energy consumption. Advances in this direction demand\nnot only experimental techniques that allow for measurements of OV dynamics,\nbut also of theoretical studies that shed light on the involved mechanisms.\nAlong this goal, we analize the OV dynamics in redox interfaces formed when an\noxidizable metallic electrode is in contact with the insulating oxide. We show\nhow the transfer of OV can be manipulated by using different electrical stimuli\nprotocols to optimize device figures such as the ON/OFF ratio or the energy\ndissipation linked to the writing process. Analytical expressions for attained\nresistance values, including the high and low resistance states are derived in\nterms of total transferred OV in a nanoscale region of the interface. Our\npredictions are validated with experiments performed in\nTi/La$_{1/3}$Ca$_{2/3}$MnO$_{3}$ redox memristive devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ramsey Interference in a Multi-level Quantum System: We report Ramsey interference in the excitonic population of a negatively\ncharged quantum dot revealing the coherence of the state in the limit where\nradiative decay is dominant. Our experiments show that the decay time of the\nRamsey interference is limited by the spectral width of the transition.\nApplying a vertical magnetic field induces Zeeman split transitions that can be\naddressed by changing the laser detuning to reveal 2, 3 and 4 level system\nbehaviour. We show that under finite field the phase-sensitive control of two\noptical pulses from a single laser can be used to prepare both population and\nspin qubits simultaneously.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum information processing with large nuclear spins in GaAs\n  semiconductors: We propose an implementation for quantum information processing based on\ncoherent manipulations of nuclear spins I=3/2 in GaAs semiconductors. We\ndescribe theoretically an NMR method which involves multiphoton transitions and\nwhich exploits the non-equidistance of nuclear spin levels due to quadrupolar\nsplittings. Starting from known spin anisotropies we derive effective\nHamiltonians in a generalized rotating frame, valid for arbitrary I, which\nallow us to describe the non-perturbative time evolution of spin states\ngenerated by magnetic rf fields. We identify an experimentally accessible\nregime where multiphoton Rabi oscillations are observable. In the nonlinear\nregime, we find Berry phase interference effects.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effect of the electromagnetic environment on current fluctuations in\n  driven tunnel junctions: We examine current fluctuations in tunnel junctions driven by a superposition\nof a constant and a sinusoidal voltage source. In standard setups the external\nvoltage is applied to the tunneling element via an impedance providing an\nelectromagnetic environment of the junction. The modes of this environment are\nexcited by the time-dependent voltage and are the source of Johnson-Nyquist\nnoise. We determine the autocorrelation function of the current flowing in the\nleads of the junction in the weak tunneling limit up to terms of second order\nin the tunneling Hamiltonian. The driven modes of the electromagnetic\nenvironment are treated exactly by means of a unitary transformation introduced\nrecently. Particular emphasis is placed on the spectral function of the current\nfluctuations. The spectrum is found to comprise three contributions: a term\narising from the Johnson-Nyquist noise of the environmental impedance, a part\ndue to the shot noise of the tunneling element and a third contribution which\ncomes from the cross-correlation between fluctuations caused by the\nelectromagnetic environment and fluctuations of the tunneling current. All\nthree parts of the spectral function occur already for devices under dc bias.\nThe spectral function of ac driven tunneling elements can be determined from\nthe result for a dc bias by means of a photo-assisted tunneling relation of the\nTien-Gordon type. Specific results are given for an Ohmic environment and for a\njunction driven through a resonator.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronics and photonics: two sciences in the benefit of solar energy\n  conversion: This paper gives a personal global point of view on two sciences: electronics\nand photonics towards plasmonics and solar energy conversion. The new research\ndirections in these two sciences are pointed out by comparison and in the\nperspective of future new solar devices. A parallel and the equivalence between\nelectronics and photonics are presented. Starting from electron in electronics,\nphoton, solitons and plasmons in photonics, electrical cables - optical fibers,\nplasmonic wave guides, electrical circuits - optical circuits, electrical\ntransistors - optical transistors, plasmonster, electrical generators - pulsed\nlasers and spasers, photonics gets step by step all the tools already existing\nin electronics. Solar energy could be converted in many ways, the most known is\nthe conversion in electricity. Today we need that the energy is in form of\nelectricity because most of the apparatus that we use are based on electricity:\ninformatics, motors, etc. However, the progress in photonics with optical\ncircuits, optical transistors etc., shows that the photonics informatics could\nbe possible. Also the optical manipulation and optical engines concept were\nalready demonstrated experimentally. If the laser propulsion will be achieved,\nand the optical engines will work, the question that will rise tomorrow is:\n\"Shall we still use the electricity in the future? What will be the solar\ndevices tomorrow?\"",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Neck Barrier Engineering in Quantum Dot Dimer Molecules via\n  Intra-Particle Ripening: Coupled colloidal quantum dot (CQD) dimers represent a new class of\nartificial molecules composed of fused core/shell semiconductor nanocrystals.\nThe electronic coupling and wavefunction hybridization is enabled by the\nformation of an epitaxial connection with a coherent lattice between the shells\nof the two neighboring quantum dots where the shell material and its dimensions\ndictate the quantum barrier characteristics for the charge carriers. Herein we\nintroduce a colloidal approach to control the neck formation at the interface\nbetween the two CQDs in such artificial molecular constructs. This allows the\ntailoring of the neck barrier in pre-linked homodimers formed via fusion of\nmultifaceted wurtzite CdSe/CdS CQDs. The effects of reaction time, temperature\nand excess ligands is studied. The neck filling process follows an\nintraparticle ripening mechanism at relatively mild reaction conditions while\navoiding inter-particle ripening. The degree of surface ligand passivation\nplays a key role in activating the surface atom diffusion to the neck region.\nThe degree of neck filling strongly depends also on the initial relative\norientation of the two CQDs, where homonymous plane attachment allows for\nfacile neck growth, unlike the case of heteronymous plane attachment. Upon\nneck-filling, the observed red-shift of the absorption and fluorescence\nmeasured both for ensemble and single dimers, is assigned to enhanced\nhybridization of the confined wavefunction in CQD dimer molecules, as supported\nby quantum calculations. The fine tuning of the particle interface introduced\nherein provides therefore a powerful tool to further control the extent of\nhybridization and coupling in CQD molecules.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Van Hove scenario of anisotropic transport in a two-dimensional\n  spin-orbit coupled electron gas in an in-plane magnetic field: We study electronic transport in two-dimensional spin-orbit coupled electron\ngas subjected to an in-plane magnetic field. The interplay of the spin-orbit\ninteraction and the magnetic field leads to the Van Hove singularity of the\ndensity of states and strong anisotropy of Fermi contours. We develop a method\nthat allows one to exactly calculate the nonequilibrium distribution function\nfor these conditions within the framework of the semiclassical Boltzmann\nequation without using the scattering time approximation. The method is applied\nto calculate the conductivity tensor and the tensor of spin polarization\ninduced by the electric field (Aronov-Lyanda-Geller-Edelstein effect). It is\nfound that both the conductivity and the spin polarization have a sharp\nsingularity as functions of the Fermi level or magnetic field, which occurs\nwhen the Fermi level passes through the Van Hove singularity. In addition, the\ntransport anisotropy dramatically changes near the singularity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum theory of an electron waiting time clock: The electron waiting time is the time that passes between two subsequent\ncharge transfers in an electronic conductor. Recently, theories of electron\nwaiting times have been devised for quantum transport in Coulomb-blockade\nstructures and for mesoscopic conductors, however, so far a proper description\nof a detector has been missing. Here we develop a quantum theory of a waiting\ntime clock capable of measuring the distribution of waiting times between\nelectrons above the Fermi sea in a mesoscopic conductor. The detector consists\nof a mesoscopic capacitor coupled to a quantum two-level system whose coherent\nprecession we monitor. Under ideal operating conditions our waiting time clock\nrecovers the results of earlier theories without a detector. We investigate\npossible deviations due to an imperfect waiting time clock. As specific\napplications we consider a quantum point contact with a constant voltage and\nlorentzian voltage pulses applied to an electrode.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effect of charged line defects on conductivity in graphene: numerical\n  Kubo and analytical Boltzmann approaches: Charge carrier transport in single-layer graphene with one-dimensional\ncharged defects is studied theoretically. Extended charged defects, considered\nan important factor for mobility degradation in chemically-vapor-deposited\ngraphene, are described by a self-consistent Thomas-Fermi potential. A\nnumerical study of electronic transport is performed by means of a\ntime-dependent real-space Kubo approach in honeycomb lattices containing\nmillions of carbon atoms, capturing the linear response of realistic size\nsystems in the highly disordered regime. Our numerical calculations are\ncomplemented with a kinetic transport theory describing charge transport in the\nweak scattering limit. The semiclassical transport lifetimes are obtained by\ncomputing scattered amplitudes within the second Born approximation. The\ntransport electron-hole asymmetry found in the semiclassical approach is\nconsistent with the Kubo calculations. In the strong scattering regime, the\nconductivity is found to be a sublinear function of electronic density and\nweakly dependent on the Thomas-Fermi screening wavelength. We attribute this\natypical behavior to the extended nature of one-dimensional charged defects.\nOur results are consistent with recent experimental reports.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Unexpected Behavior of the Local Compressibility Near the B=0\n  Metal-Insulator Transition: We have measured the local electronic compressibility of a two-dimensional\nhole gas as it crosses the B=0 Metal-Insulator Transition. In the metallic\nphase, the compressibility follows the mean-field Hartree-Fock (HF) theory and\nis found to be spatially homogeneous. In the insulating phase it deviates by\nmore than an order of magnitude from the HF predictions and is spatially\ninhomogeneous. The crossover density between the two types of behavior, agrees\nquantitatively with the transport critical density, suggesting that the system\nundergoes a thermodynamic change at the transition.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Evolution of the Spin Hall Magnetoresistance in Cr$_2$O$_3$/Pt bilayers\n  close to the N\u00e9el temperature: We study the evolution of magnetoresistance with temperature in thin film\nbilayers consisting of platinum and the antiferromagnet Cr$_2$O$_3$ with its\neasy axis out of the plane. We vary the temperature from 20 - 60{\\deg}C, close\nto the N\\'eel temperature of Cr$_2$O$_3$ of approximately 37{\\deg}C. The\nmagnetoresistive response is recorded during rotations of the external magnetic\nfield in three mutually orthogonal planes. A large magnetoresistance having a\nsymmetry consistent with a positive spin Hall magnetoresistance is observed in\nthe paramagnetic phase of the Cr$_2$O$_3$, which however vanishes when cooling\nto below the N\\'eel temperature. Comparing to analogous experiments in a\nGd$_3$Ga$_5$O$_{12}$/Pt heterostructure, we conclude that a paramagnetic field\ninduced magnetization in the insulator is not sufficient to explain the\nobserved magnetoresistance. We speculate that the type of magnetic moments at\nthe interface qualitatively impacts the spin angular momentum transfer, with\nthe $3d$ moments of Cr sinking angular momentum much more efficiently as\ncompared to the more localized $4f$ moments of Gd.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Localized States and Quantum Spin Hall Effect in Si-Doped InAs/GaSb\n  Quantum Wells: We study localized in-gap states and quantum spin Hall effect in Si-doped\nInAs/GaSb quantum wells. We propose a model describing donor and/or acceptor\nimpurities to describe Si dopants. This model shows in-gap bound states and\nwide conductance plateau with the quantized value $2e^2/h$ in light dopant\nconcentration, consistent with recent experiments by Du et al. We predict a\nconductance dip structure due to backward scattering in the region where the\nlocalization length $\\xi$ is comparable with the sample width $L_y$ but much\nsmaller than the sample length $L_x$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Escape from a zero current state in a one dimensional array of Josephson\n  junctions: A long one dimensional array of small Josephson junctions exhibits Coulomb\nblockade of Cooper pair tunneling. This zero current state exists up to a\nswitching voltage, Vsw, where there is a sudden onset of current. In this paper\nwe present histograms showing how Vsw changes with temperature for a long array\nand calculations of the corresponding escape rates. Our analysis of the problem\nis based on the existence of a voltage dependent energy barrier and we do not\nmake any assumptions about its shape. The data divides up into two temperature\nregimes, the higher of which can be explained with Kramers thermal escape\nmodel. At low temperatures the escape becomes independent of temperature.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological classification of the single-wall carbon nanotube: The single-wall carbon nanotube (SWNT) can be a one-dimensional topological\ninsulator, which is characterized by a $\\mathbb{Z}$-topological invariant,\nwinding number. Using the analytical expression for the winding number, we\nclassify the topology for all possible chiralities of SWNTs in the absence and\npresence of a magnetic field, which belongs to the topological categories of\nBDI and AIII, respectively. We find that the majority of SWNTs are nontrivial\ntopological insulators in the absence of a magnetic field. In addition, the\ntopological phase transition takes place when the band gap is closed by\napplying a magnetic field along the tube axis, in all the SWNTs except armchair\nnanotubes. The winding number determines the number of edge states localized at\nthe tube ends by the bulk-edge correspondence, the proof of which is given for\nSWNTs in general. This enables the identification of the topology in\nexperiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tuning the magnetic configuration of bilayer graphene quantum dot by\n  twisting: Twistronic has recently attracted tremendous attention because the twisting\ncan engineer the bilayer graphene-like materials into varying types of strongly\ncorrelated phases. In this paper, we study the twisting of bilayer graphene\n(BLG) quantum dots (QDs) with hexagonal shape and zigzag edges. In the\nuntwisted BLG-QDs, the zigzag edges of graphene host spontaneous magnetism with\nvarying magnetic configurations. As a BLG-QD being adiabatically twisted, the\nquantum state evolves as a function of the twisting angle. If the twisting\nangle changes across certain critical value, the magnetic configuration of the\nquantum state sharply changes. For the twisting process with increasing or\ndecreasing twisting angle, the number and value of the critical twisting angles\nare different. Thus, the twisting process with the twisting angle increasing\nand decreasing back and forth could enter a hysteresis loop. The twisting of\nBLG QDs with adatom is also investigated. The tuning features of the magnetic\nconfiguration of the twisted BLG-QDs could be applied for graphene-based\nquantum memory devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Photoluminescence in PbS nanocrystal thin films: Nanocrystal density,\n  film morphology and energy transfer: We show that photoluminescence properties of PbS nanocrystal thin films are\ndirectly related to film morphology and nanocrystal density. In densely packed\nPbS nanocrystal films, low-temperature donor-to-acceptor energy transfer is\nmainly responsible for the photoluminescence spectra narrowing and shift toward\nlonger wavelengths. At elevated temperatures, back energy transfer is proposed\nto be responsible for an unusual photoluminescence intensity temperature\ndependence. In thin films with a low PbS nanocrystal density, the energy\ntransfer is suppressed, and the effect is dramatically reduced.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Gate-Controlled Magnetoresistance of a Paramagnetic Insulator|Platinum\n  Interface: We report an electric field-induced in-plane magnetoresistance of an\natomically flat paramagnetic insulator|platinum (Pt) interface at low\ntemperatures with an ionic liquid gate. Transport experiments as a function of\napplied magnetic field strength and direction obey the spin Hall\nmagnetoresistance phenomenology with perpendicular magnetic anisotropy. Our\nresults establish the utility of ionic gating as an alternative method to\ncontrol spintronic devices without using ferromagnets.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Deterministic Weak Localization in Periodic Structures: The weak localization is found for perfect periodic structures exhibiting\ndeterministic classical diffusion. In particular, the velocity autocorrelation\nfunction develops a universal quantum power law decay at 4 times Ehrenfest\ntime, following the classical stretched-exponential type decay. Such\ndeterministic weak localization is robust against weak enough randomness (e.g.,\nquantum impurities). In the 1D and 2D cases, we argue that at the quantum limit\nstates localized in the Bravis cell are turned into Bloch states by quantum\ntunnelling.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electrical transport in deformed nanostrips: electrical signature of\n  reversible mechanical failure: We calculate the electrical conductivity of a thin crystalline strip of atoms\nconfined within a quasi one dimensional channel of fixed width. The\nconductivity shows anomalous behavior as the strip is deformed under tensile\nloading. Beyond a critical strain, the solid fails by the nucleation of\nalternating bands of solid and {\\em smectic} like phases accompanied by a jump\nin the conductivity. Since the failure of the strip in this system is known to\nbe reversible, the onductivity anomaly may have practical use as a sensitive\nstrain transducer.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spatially dispersive dynamical response of hot carriers in doped\n  graphene: We study theoretically wave-vector and frequency dispersion of the complex\ndynamic conductivity tensor (DCT), $\\sigma_{lm}(\\mathbf{k}, \\omega)$, of doped\nmonolayer graphene under a strong dc electric field. For a general analysis, we\nconsider the weak ac field of arbitrary configuration given by two independent\nvectors, the ac field polarization and the wave vector $\\mathbf{k}$. The\nhigh-field transport and linear response to the ac field are described on the\nbase of the Boltzmann kinetic equation. We show that the real part of DCT,\ncalculated in the collisionless regime, is not zero due to dissipation of the\nac wave, whose energy is absorbed by the resonant Dirac quasiparticles\neffectively interacting with the wave. The role of the kinematic resonance at\n$\\omega = v_F |{\\bf k}|$ ($v_{F}$ is the Fermi velocity) is studied in detail\ntaking into account deviation from the linear energy spectrum and screening by\nthe charge carriers. The isopower-density curves and distributions of angle\nbetween the ac current density and field vectors are presented as a map which\nprovides clear graphic representation of the DCT anisotropy. Also, the map\nshows certain ac field configurations corresponding to a negative power\ndensity, thereby it indicates regions of terahertz frequency for possible\nelectrical (drift) instability in the graphene system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Material Parameters for Faster Ballistic Switching of an In-plane\n  Magnetized Nanomagnet: High-speed magnetization switching of a nanomagnet is necessary for faster\ninformation processing. The ballistic switching by a pulsed magnetic filed is a\npromising candidate for the high-speed switching. It is known that the\nswitching speed of the ballistic switching can be increased by increasing the\nmagnitude of the pulsed magnetic field. However it is difficult to generate a\nstrong and short magnetic field pulse in a small device. Here we explore\nanother direction to achieve the high-speed ballistic switching by designing\nmaterial parameters such as anisotropy constant, saturation magnetization, and\nthe Gilbert damping constant. We perform the macrospin simulations for the\nballistic switching of in-plane magnetized nano magnets with varying material\nparameters. The results are analyzed based on the switching dynamics on the\nenergy density contour. We show that the pulse width required for the ballistic\nswitching can be reduced by increasing the magnetic anisotropy constant or by\ndecreasing the saturation magnetization. We also show that there exists an\noptimal value of the Gilbert damping constant that minimizes the pulse width\nrequired for the ballistic switching.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Temperature-linear Resistivity in Twisted Double Bilayer Graphene: We report an experimental study of carrier density (n), displacement field\n(D) and twist angle ({\\theta}) dependence of temperature (T)-linear resistivity\nin twisted double bilayer graphene (TDBG). For a large twist angle\n({\\theta}>1.5{\\deg}) where correlated insulating states are absent, we observe\na T-linear resistivity (with the slope of the order ~10{\\Omega}/K) over a wide\nrange of carrier density and its slope decreases with increasing of n, in\nagreement with acoustic phonon scattering model semi-quantitatively. The slope\nof T-linear resistivity is non-monotonically dependent on the displacement\nfield with a single peak structure. For device with {\\theta}~1.23{\\deg} at\nwhich correlated states emerge, the slope of T-linear resistivity is found\nmaximum (~100{\\Omega}/K) at the boundary of the halo structure where phase\ntransition occurs, with signatures of continuous phase transition, Planckian\ndissipation, and the diverging effective mass; these observations are in line\nwith quantum critical behaviors, which might be due to the symmetry-breaking\ninstability at the critical points. Our results shed new light on correlated\nphysics in TDBG and other twisted moir\\'e systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electric field effects on the band gap and edge states of monolayer\n  1T'-WTe2: Monolayer 1T'-WTe2 is a quantum spin Hall insulator with a gapped bulk and\ngapless helical edge states persisting to temperatures around 100 K. Recent\nstudies have revealed a topological-to-trivial phase transition as well the\nemergence of an unconventional, potentially topological superconducting state\nupon tuning the carrier concentration with gating. However, despite extensive\nstudies, the effects of gating on the band structure and the helical edge\nstates have not yet been established. In this work we present a combined\nlow-temperature STM and first principles study of back-gated monolayer 1T'-WTe2\nfilms grown on graphene. Consistent with a quantum spin Hall system, the films\nshow well-defined bulk gaps and clear edge states that span the gap. By\ndirectly measuring the density of states with STM spectroscopy, we show that\nthe bulk band gap magnitude shows substantial changes with applied gate\nvoltage, which is contrary to the na\\\"ive expectation that a gate would rigidly\nshift the bands relative to the Fermi level. To explain our data, we carry out\ndensity functional theory and model Hamiltonian calculations which show that a\ngate electric field causes doping and inversion symmetry breaking which\npolarizes and spin-splits the bulk bands. Interestingly, the calculated spin\nsplitting from the effective Rashba-like spin-orbit coupling can be in the tens\nof meV for the electric fields in the experiment, which may be useful for\nspintronics applications. Our work reveals the strong effect of electric fields\non the bulk band structure of monolayer 1T'-WTe2, which will play a critical\nrole in our understanding of gate-induced phenomena in this system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Valley filters using graphene blister defects from first principles: Valleytronics, which makes use of the two valleys in graphenes, attracts\nconsiderable attention and a valley filter is expected to be the central\ncomponent in valleytronics. We propose the application of the graphene valley\nfilter using blister defects to the investigation of the valley-dependent\ntransport properties of the Stone--Wales and blister defects of graphenes by\ndensity functional theory calculations. It is found that the intervalley\ntransition from the $\\mathbf{K}$ valley to the $\\mathbf{K}^\\prime$ valleys is\ncompletely suppressed in some defects. Using a large bipartite honeycomb cell\nincluding several carbon atoms in a cell and replacing atomic orbitals with\nmolecular orbitals in the tight-binding model, we demonstrate analytically and\nnumerically that the symmetry between the A and B sites of the bipartite\nhoneycomb cell contributes to the suppression of the intervalley transition. In\naddition, the universal rule for the atomic structures of the blisters\nsuppressing the intervalley transition is derived. Furthermore, by introducing\nadditional carbon atoms to graphenes to form blister defects, we can split the\nenergies of the states at which resonant scattering occurs on the $\\mathrm{K}$\nand $\\mathrm{K}^\\prime$ channel electrons. Because of this split, the fully\nvalley-polarized current will be achieved by the local application of a gate\nvoltage.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mesoscopic to universal crossover of transmission phase of multi-level\n  quantum dots: Transmission phase \\alpha measurements of many-electron quantum dots (small\nmean level spacing \\delta) revealed universal phase lapses by \\pi between\nconsecutive resonances. In contrast, for dots with only a few electrons (large\n\\delta), the appearance or not of a phase lapse depends on the dot parameters.\nWe show that a model of a multi-level quantum dot with local Coulomb\ninteractions and arbitrary level-lead couplings reproduces the generic features\nof the observed behavior. The universal behavior of \\alpha for small \\delta\nfollows from Fano-type antiresonances of the renormalized single-particle\nlevels.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic field induces giant nonlinear optical response in Weyl\n  semimetals: We study the second-order optical response of Weyl semimetals in the presence\nof a magnetic field. We consider an idealized model of a perfectly linear Weyl\nnode and use the Kubo formula at zero temperature to calculate the intrinsic\ncontribution to photocurrent and second harmonic generation conductivity\ncomponents. We obtain exact analytical expressions applicable at arbitrary\nvalues of frequency, chemical potential, and magnetic field. Our results show\nthat finite magnetic field significantly enhances the nonlinear optical\nresponse in semimetals, while magnetic resonances lead to divergences in\nnonlinear conductivity. In realistic systems, these singularities are\nregularized by a finite scattering rate, but result in pronounced peaks which\ncan be detected experimentally, provided the system is clean and interactions\nare weak. We also perform a semiclassical calculation that complements and\nconfirms our microscopic results at small magnetic fields and frequencies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Low-field magnetotransport in graphene cavity devices: Confinement and edge structures are known to play significant roles in\nelectronic and transport properties of two-dimensional materials. Here, we\nreport on low-temperature magnetotransport measurements of lithographically\npatterned graphene cavity nanodevices. It is found that the evolution of the\nlow-field magnetoconductance characteristics with varying carrier density\nexhibits different behaviors in graphene cavity and bulk graphene devices. In\nthe graphene cavity devices, we have observed that intravalley scattering\nbecomes dominant as the Fermi level gets close to the Dirac point. We associate\nthis enhanced intravalley scattering to the effect of charge inhomogeneities\nand edge disorder in the confined graphene nanostructures. We have also\nobserved that the dephasing rate of carriers in the cavity devices follows a\nparabolic temperature dependence, indicating that the direct Coulomb\ninteraction scattering mechanism governs the dephasing at low temperatures. Our\nresults demonstrate the importance of confinement in carrier transport in\ngraphene nanostructure devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Skyrmion Brownian circuit implemented in a continuous ferromagnetic thin\n  film: The fabrication of a skyrmion circuit which stabilizes skyrmions is important\nto realize micro- to nano-sized skyrmion devices. One example of promising\nskyrmion-based device is Brownian computers, which have been theoretically\nproposed, but not realized. It would require a skyrmion circuit in which the\nskyrmion is stabilized and easily movable. However, the usual skyrmion circuits\nfabricated by etching of the ferromagnetic film decrease the demagnetization\nfield stabilizing the skyrmions, and thus prevent their formation. In this\nstudy, a skyrmion Brownian circuit implemented in a continuous ferromagnetic\nfilm with patterned SiO$_2$ capping to stabilize the skyrmion formation. The\npatterned SiO$_2$ capping controls the saturation field of the ferromagnetic\nlayer and forms a wire-shaped skyrmion potential well, which stabilizes\nskyrmion formation in the circuit. Moreover, we implement a hub (Y-junction)\ncircuit without pinning sites at the junction by patterned SiO$_2$ capping.\nThis technique enables the efficient control of skyrmion-based memory and logic\ndevices, as well as Brownian computers.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thickness and electric field dependent polarizability and dielectric\n  constant in phosphorene: Based on extensive first principle calculations, we explore the thickness\ndependent effective di- electric constant and slab polarizability of few layer\nblack phosphorene. We find that the dielectric constant in ultra-thin\nphosphorene is thickness dependent and it can be further tuned by applying an\nout of plane electric field. The decreasing dielectric constant with reducing\nnumber of layers of phosphorene, is a direct consequence of the lower\npermittivity of the surface layers and the in- creasing surface to volume\nratio. We also show that the slab polarizability depends linearly on the number\nof layers, implying a nearly constant polarizability per phosphorus atom. Our\ncalculation of the thickness and electric field dependent dielectric properties\nwill be useful for designing and interpreting transport experiments in gated\nphosphorene devices, wherever electrostatic effects such as capacitance, charge\nscreening etc. are important.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunable spin and transport in porphyrin-graphene nanoribbon hybrids: Recently, porphyrin units have been attached to graphene nanoribbons\n(Por-GNR) enabling a multitude of possible structures. Here we report first\nprinciples calculations of two prototypical, experimentally feasible, Por-GNR\nhybrids, one of which displays a small band gap relevant for its use as\nelectrode in a device. Embedding a Fe atom in the porphyrin causes spin\npolarization with a spin ground state $S=1$. We employ density functional\ntheory and nonequilibrium Green's function transport calculations to examine a\n2-terminal setup involving one Fe-Por-GNR between two metal-free, small band\ngap, Por-GNR electrodes. The coupling between the Fe-$d$ and GNR band states\nresults in a Fano anti-resonance feature in the spin transport close to the\nFermi energy. This feature makes transport highly sensitive to the Fe spin\nstate. We demonstrate how mechanical strain or chemical adsorption on the Fe\ngive rise to a spin-crossover to $S=1$ and $S=0$, respectively, directly\nreflected in a change in transport. Our theoretical results provide a clue for\nthe on-surface synthesis of Por-GNRs hybrids, which can open a new avenue for\ncarbon-based spintronics and chemical sensing.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Control of charging in resonant tunneling through InAs nanocrystal\n  quantum dots: Tunneling spectroscopy of InAs nanocrystals deposited on graphite was\nmeasured using scanning tunneling microscopy, in a double-barrier\ntunnel-junction configuration. The effect of the junction symmetry on the\ntunneling spectra is studied experimentally and modeled theoretically. When the\ntip is retracted, we observe resonant tunneling through the nanocrystal states\nwithout charging. This is in contrast to previous measurements on similar\nnanocrystals anchored to gold by linker molecules, where charging took place.\nCharging is regained upon reducing the tip-nanocrystal distance, making the\njunctions more symmetric. The effect of voltage distribution between the\njunctions on the measured spectra is also discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum transport in flat bands and super-metallicity: Quantum physics in flat-band (FB) systems embodies a variety of exotic\nphenomenon and even counter intuitive features. The quantum transport in\nseveral graphene based compounds that exhibit a flat band and a tunable gap is\ninvestigated. Despite the localized nature of the FB states and a zero group\nvelocity, a super-metallic (SM) phase at the FB energy is revealed. The SM\nphase is robust against the inelastic scattering strength and controlled only\nby the inter-band transitions between the FB and the dispersive bands. The SM\nphase appears insensitive and quasi independent of the gap amplitude and nature\nof the lattice (disordered or nano-patterned). The universal nature of the\nunconventional FB transport is illustrated with the case of electrons in the\nLieb lattice.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cotunneling effects in GaAs vertical double quantum dot: We observed lifting of Coulomb blockade in GaAs vertical double quantum dot\nwith low potential barriers, induced by cotunneling mechanisms at dilution\nfridge temperature of 10 mK. Several distinct features were observed, compared\nto single dot case, and appropriate explanation for them was given",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin dynamics and spin-dependent recombination of a polaron pair under a\n  strong ac drive: We study theoretically the recombination within a pair of two polarons in\nmagnetic field subject to a strong linearly polarized ac drive. Strong drive\nimplies that the Zeeman frequencies of the pair-partners are much smaller than\nthe Rabi frequency, so that the rotating wave approximation does not apply.\nWhat makes the recombination dynamics nontrivial, is that the partners\nrecombine only when they form a singlet, S. By admixing singlet to triplets,\nthe drive induces the triplet recombination as well. We calculate the effective\ndecay rate of all four spin modes. Our main finding is that, under the strong\ndrive, the major contribution to the decay of the modes comes from short time\nintervals when the driving field passes through zero. When the recombination\ntime in the absence of drive is short, fast recombination from S leads to\nanomalously slow recombination from the other spin states of the pair. We show\nthat, with strong drive, this recombination becomes even slower. The\ncorresponding decay rate falls off as a power law with the amplitude of the\ndrive.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fast and slow edges in bilayer graphene nanoribbons: Tuning the\n  transition from band- to Mott-insulator: We show that gated bilayer graphene zigzag ribbons possess a fast and a slow\nedge, characterized by edge state velocities that differ due to non-negligible\nnext-nearest-neighbor hopping elements. By applying bosonization and\nrenormalization group methods, we find that the slow edge can acquire a sizable\ninteraction-induced gap, which is tunable via an external gate voltage V_{g}.\nIn contrast to the gate-induced gap in the bulk, the interaction-induced gap\ndepends non-monotonously on the on-site potential V.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Designer quantum states of matter created atom-by-atom: With the advances in high resolution and spin-resolved scanning tunneling\nmicroscopy as well as atomic-scale manipulation, it has become possible to\ncreate and characterize quantum states of matter bottom-up, atom-by-atom. This\nis largely based on controlling the particle- or wave-like nature of electrons,\nas well as the interactions between spins, electrons, and orbitals and their\ninterplay with structure and dimensionality. We review the recent advances in\ncreating artificial electronic and spin lattices that lead to various exotic\nquantum phases of matter, ranging from topological Dirac dispersion to complex\nmagnetic order. We also project future perspectives in non-equilibrium\ndynamics, prototype technologies, engineered quantum phase transitions and\ntopology, as well as the evolution of complexity from simplicity in this newly\ndeveloping field.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Reaction diffusion dynamics and the Schryer-Walker solution for domain\n  walls of the Landau-Lifshitz-Gilbert equation: We study the dynamics of the equation obtained by Schryer and Walker for the\nmotion of domain walls. The reduced equation is a reaction diffusion equation\nfor the angle between the applied field and the magnetization vector. If the\nhard axis anisotropy $K_d$ is much larger than the easy axis anisotropy $K_u$,\nthere is a range of applied fields where the dynamics does not select the\nSchryer-Walker solution. We give analytic expressions for the speed of the\ndomain wall in this regime and the conditions for its existence.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Formation of image-potential states at the graphene/metal interface: The formation of image-potential states at the interface between a graphene\nlayer and a metal surface is studied by means of model calculations. An\nanalytical one-dimensional model-potential for the combined system is\nconstructed and used to calculate energies and wave functions of the\nimage-potential states at the Gamma-point as a function of the graphene-metal\ndistance. It is demonstrated how the double series of image-potential states of\nfree-standing graphene evolves into interfacial states that interact with both\nsurfaces at intermediate distances and finally into a single series of states\nresembling those of a clean metal surface covered by a monoatomic spacer layer.\nThe model quantitatively reproduces experimental data available for\ngraphene/Ir(111) and graphene/Ru(0001), systems which strongly differ in\ninteraction strength and therefore adsorption distance. Moreover, it provides a\nclear physical explanation for the different binding energy and lifetime of the\nfirst (n=1) image-potential state in the valley and hill areas of the strongly\ncorrugated moire superlattice of graphene/Ru(0001).",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Full counting statistics of information content and particle number: We consider a bipartite quantum conductor and discuss the joint probability\ndistribution of particle number in a subsystem and the self-information\nassociated with the reduced density matrix of the subsystem. By extending the\nmulti-contour Keldysh Green function technique, we calculate the R\\'enyi\nentropy of a positive integer order $M$ subjected to the particle number\nconstraint, from which we derive the joint probability distribution. For\nenergy-independent transmission, we derive the time dependence of the\naccessible entanglement entropy, or the conditional entropy. We analyze the\njoint probability distribution for energy-dependent transmission probability at\nthe steady state under the coherent resonant tunneling and the incoherent\nsequential tunneling conditions. We also discuss the probability distribution\nof the efficiency, which measures the information content transfered by a\nsingle electron.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ultrafast excitation and topological soliton formation in incommensurate\n  charge density wave states: Topological soliton is a nonperturbative excitation in commensurate density\nwave states and connects degenerate ground states. In incommensurate density\nwave states, ground states are continuously degenerate and topological soliton\nis reckoned to be smoothly connected to the perturbative phason excitation. We\nstudy the ultrafast nonequilibrium dynamics due to photoexcited electron-hole\npair in a one-dimensional chain with an incommensurate charge density wave\nground state. Time-resolved evolution reveals both perturbative excitation of\ncollective modes and nonperturbative topological phase transition due to\ncreating novel topological solitons, where the continuous complex order\nparameter with amplitude and phase is essential. We identify the nontrivial\nphase-winding solitons in the complex plane unique to this nonequilibrium state\nand capture it by a low-energy effective model. The perturbative temporal gap\noscillation and the solitonic in-gap states enter the optical conductivity\nabsorption edge and the spectral density related to spectroscopic measurement,\nproviding concrete connections to real experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Controlling the conductance of molecular wires by defect engineering: a\n  divide et impera approach: Understanding of charge transport mechanisms in nanoscale structures is\nessential for the development of molecular electronic devices. Charge transport\nthrough 1D molecular systems connected between two contacts is influenced by\nseveral parameters such as the electronic structure of the molecule and the\npresence of disorder and defects. In this work, we have modeled 1D molecular\nwires connected between electrodes and systematically investigated the\ninfluence of both soliton formation and the presence of defects on properties\nsuch as the conductance and the density of states. Our numerical calculations\nhave shown that the transport properties are highly sensitive to the position\nof both solitons and defects. Interestingly, the introduction of a single\ndefect in the molecular wire which divides it into two fragments both\nconsisting of an odd number of sites creates a new conduction channel in the\ncenter of the band gap resulting in higher zero-bias conductance than for\ndefect free systems. This phenomenon suggests alternative routes toward\nengineering molecular wires with enhanced conductance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermodynamic Properties of Graphene in Magnetic Field and Rashba\n  Coupling: We study the thermodynamic properties of massless Dirac fermions in graphene\nsubjected to a uniform magnetic field $B$ together with Rashba coupling\nparameter $\\lambda_R$. The thermodynamic functions such as the Helmholtz free\nenergy, total energy, entropy and heat capacity are obtained in the high\ntemperature regime using an approach based on the zeta function. These\nfunctions will be numerically examined by considering two cases related to\n$\\lambda_R$ smaller or greater than $B$. In particular, we show that the\nDulong-Petit law is verified for both cases.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Driven Andreev molecule: We study the three terminal S-QD-S-QD-S Josephson junction biased with\ncommensurate voltages. In the absence of an applied voltage, the Andreev bound\nstates on each quantum dot hybridize forming an `Andreev molecule'. However,\nunderstanding of this system in a non-equilibrium setup is lacking. Applying a\ndc voltage on the bijunction makes the system time-periodic, and the\nequilibrium Andreev bound states evolve into a ladder of resonances with a\nfinite lifetime due to multiple Andreev reflections (MAR). Starting from the\ntime-periodic Bogoliubov-de Gennes equations we map the problem to a\ntight-binding chain in the (infinite) Floquet space. The resolvent of this\nnon-Hermitian block matrix is obtained via a continued fraction method. We\nnumerically calculate the Floquet-Andreev spectra which could be probed by\nlocal tunneling spectroscopy on the dots. We also consider the subgap current,\nand show that the Floquet resonances determine the position of the MAR steps.\nProximity of the two dots causes splitting of the steps, while at large\ndistances we observe interference effects which cause oscillations in the I-V\ncurves. The latter effect should persist at very long distances.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bloch-point-mediated topological transformations of magnetic domain\n  walls in cylindrical nanowires: Cylindrical nanowires made of soft magnetic materials, in contrast to thin\nstrips, may host domain walls of two distinct topologies. Unexpectedly, we\nevidence experimentally the dynamic transformation of topology upon wall motion\nabove a field threshold. Micromagnetic simulations highlight the underlying\nprecessional dynamics for one way of the transformation, involving the\nnucleation of a Bloch-point singularity, however, fail to reproduce the reverse\nprocess. This rare discrepancy between micromagnetic simulations and\nexperiments raises fascinating questions in material and computer science.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Excited-state spectroscopy on a quantum dot side-coupled to a quantum\n  wire: We report excited-state spectroscopy on a quantum dot side-coupled to a\nquantum wire with accurate energy estimation. Our method utilizes periodic\nvoltage pulses on the dot, and the energy calibration is performed with\nreference to the bias voltage across the wire. We demonstrate the observation\nof the orbital excited state and the Zeeman splitting in a single dot.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fragility of spectral flow for topological phases in non-Wigner-Dyson\n  classes: Topological insulators and superconductors support extended surface states\nprotected against the otherwise localizing effects of static disorder.\nSpecifically, in the Wigner-Dyson insulators belonging to the symmetry classes\nA, AI, and AII, a band of extended surface states is continuously connected to\na likewise extended set of bulk states forming a ``bridge'' between different\nsurfaces via the mechanism of spectral flow. In this work we show that this\nprinciple becomes \\emph{fragile} in the majority of non-Wigner-Dyson\ntopological superconductors and chiral topological insulators. In these\nsystems, there is precisely one point with granted extended states, the center\nof the band, $E=0$. Away from it, states are spatially localized, or can be\nmade so by the addition of spatially local potentials. Considering the\nthree-dimensional insulator in class AIII and winding number $\\nu=1$ as a\nparadigmatic case study, we discuss the physical principles behind this\nphenomenon, and its methodological and applied consequences. In particular, we\nshow that low-energy Dirac approximations in the description of surface states\ncan be treacherous in that they tend to conceal the localizability phenomenon.\nWe also identify markers defined in terms of Berry curvature as measures for\nthe degree of state localization in lattice models, and back our analytical\npredictions by extensive numerical simulations. A main conclusion of this work\nis that the surface phenomenology of non-Wigner-Dyson topological insulators is\na lot richer than that of their Wigner-Dyson siblings, extreme limits being\nspectrum wide quantum critical delocalization of all states vs. full\nlocalization except at the $E=0$ critical point. As part of our study we\nidentify possible experimental signatures distinguishing between these\ndifferent alternatives in transport or tunnel spectroscopy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-orbit coupled transport and spin torque in a ferromagnetic\n  heterostructure: Ferromagnetic heterostructures provide an ideal platform to explore the\nnature of spin-orbit torques arising from the interplay mediated by itinerant\nelectrons between a Rashba-type spin-orbit coupling and a ferromagnetic\nexchange interaction. For such a prototypic system, we develop a set of coupled\ndiffusion equations to describe the diffusive spin dynamics and spin-orbit\ntorques. We characterize the spin torque and its two prominent--out-of-plane\nand in-plane--components for a wide range of relative strength between the\nRashba coupling and ferromagnetic exchange. The symmetry and angular dependence\nof the spin torque emerging from our simple Rashba model is in an agreement\nwith experiments. The spin diffusion equation can be generalized to incorporate\ndynamic effect such as spin pumping and magnetic damping.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cotunneling thermopower of single electron transistors: We study the thermopower of a quantum dot weakly coupled to two reservoirs by\ntunnel junctions. At low temperatures the transport through the dot is\nsuppressed by charging effects (Coulomb blockade). As a result the thermopower\nshows an oscillatory dependence on the gate voltage. We study this dependence\nin the limit of low temperatures where the transport through the dot is\ndominated by the processes of inelastic cotunneling. We also obtain a crossover\nformula for intermediate temperatures which connects our cotunneling results to\nthe known sawtooth behavior in the sequential tunneling regime. As the\ntemperature is lowered, the amplitude of thermopower oscillations increases,\nand their shape changes qualitatively.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Atomically thin quantum light emitting diodes: Transition metal dichalcogenides (TMDs) are optically active layered\nmaterials providing potential for fast optoelectronics and on-chip photonics.\nWe demonstrate electrically driven single-photon emission from localised sites\nin tungsten diselenide (WSe2) and tungsten disulphide (WS2). To achieve this,\nwe fabricate a light emitting diode structure comprising single layer graphene,\nthin hexagonal boron nitride and TMD mono- and bi-layers. Photon correlation\nmeasurements are used to confirm the single-photon nature of the spectrally\nsharp emission. These results present the TMD family as a platform for hybrid,\nbroadband, atomically precise quantum photonics devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The Parallel Magnetoconductance of Interacting Electrons in a Two\n  Dimensional Disordered System: The transport properties of interacting electrons for which the spin degree\nof freedom is taken into account are numerically studied for small two\ndimensional diffusive clusters. On-site electron-electron interactions tend to\ndelocalize the electrons, while long-range interactions enhance localization.\nOn careful examination of the transport properties, we reach the conclusion\nthat it does not show a two dimensional metal insulator transition driven by\ninteractions. A parallel magnetic field leads to enhanced resistivity, which\nsaturates once the electrons become fully spin polarized. The strength of the\nmagnetic field for which the resistivity saturates decreases as electron\ndensity goes down. Thus, the numerical calculations capture some of the\nfeatures seen in recent experimental measurements of parallel\nmagnetoconductance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strong gate-tunability of flat bands in bilayer graphene due to moir\u00e9\n  encapsulation between hBN monolayers: When using hexagonal boron-nitride (hBN) as a substrate for graphene, the\nresulting moir\\'e pattern creates secondary Dirac points. By encapsulating a\nmultilayer graphene within aligned hBN sheets the controlled moir\\'e stacking\nmay offer even richer benefits. Using advanced tight-binding simulations on\natomistically-relaxed heterostructures, here we show that the gap at the\nsecondary Dirac point can be opened in selected moir\\'e-stacking\nconfigurations, and is independent of any additional vertical gating of the\nheterostructure. On the other hand, gating can broadly tune the gap at the\nprincipal Dirac point, and may thereby strongly compress the first moir\\'e\nmini-band in width against the moir\\'e-induced gap at the secondary Dirac\npoint. We reveal that in hBN-encapsulated bilayer graphene this novel mechanism\ncan lead to isolated bands flatter than 10~meV under moderate gating, hence\npresenting a convenient pathway towards electronically-controlled\nstrongly-correlated states on demand.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The Edge-State Theory of Integer-Quantum-Hall-Effect to Insulator\n  Transition: Direct transitions, driven by disorder, from several integral quantum Hall\nstates to an insulator have been observed in experiment. This finding is\nenigmatic in light of a theoretical phase diagram, based on rather general\nconsiderations, that predicts a sequence of transitions in which the integer\n$n$ characterizing the Hall conductivity is reduced successively by unity,\neventually going from $n=1$ into an insulator. In this work, we suggest that\nthe direct transition occurs because, in certain parameter regime, the edge\nstates of different Landau levels are strongly coupled and behave as a single\nedge state. It is indicated under what conditions successive transitions may be\nseen.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Fluctuations along Symmetry Crossover in Kondo-correlated\n  Quantum Dot: Universal properties of entangled many-body states are controlled by their\nsymmetry and quantum fluctuations. By magnetic-field tuning of the spin-orbital\ndegeneracy in a Kondo-correlated quantum dot, we have modified quantum\nfluctuations to directly measure their influence on the many-body properties\nalong the crossover from $SU(4)$ to $SU(2)$ symmetry of the ground state.\nHigh-sensitive current noise measurements combined with the non-equilibrium\nFermi liquid theory clarify that the Kondo resonance and electron correlations\nare enhanced as the fluctuations, measured by the Wilson ratio, increase along\nthe symmetry crossover. Our achievement demonstrates that non-linear noise\nconstitutes a measure of quantum fluctuations that can be used to tackle\nquantum phase transitions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bundling dynamics regulates the active mechanics and transport in carbon\n  nanotube networks: High-density carbon nanotube networks (CNNs) continue to attract interest as\nactive elements in nanoelectronic devices, nanoelectromechanical systems (NEMS)\nand multifunctional nanocomposites. The interplay between the network\nnanostructure and the its properties is crucial, yet current understanding\nremains limited to the passive response. Here, we employ a novel superstructure\nconsisting of millimeter-long vertically aligned singe walled carbon nanotubes\n(SWCNTs) sandwiched between polydimethylsiloxane (PDMS) layers to quantify the\neffect of two classes of mechanical stimuli, film densification and stretching,\non the electronic and thermal transport across the network. The network deforms\neasily with increase in electrical and thermal conductivities suggestive of\nfloppy yet highly reconfigurable network. Insight from atomistically informed\ncoarse-grained simulations uncover an interplay between the extent of lateral\nassembly of the bundles, modulated by surface zipping/unzipping, and the\nelastic energy associated with the bent conformations of the nanotubes/bundles.\nDuring densification, the network becomes highly interconnected yet we observe\na modest increase in bundling primarily due to the reduced spacing between the\nSWCNTs. The stretching, on the other hand, is characterized by an initial\ndebundling regime as the strain accommodation occurs via unzipping of the\nbranched interconnects, followed by rapid re-bundling as the strain transfers\nto the increasingly aligned bundles. In both cases, the increase in the\nelectrical and thermal conductivity is primarily due to the increase in bundle\nsize; the changes in network connectivity have a minor effect on the transport.\nOur results have broad implications for filamentous networks of inorganic\nnanoassemblies composed of interacting tubes, wires and ribbons/belts.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Theoretical Investigation of Local Electron Temperature in Quantum Hall\n  Systems: In this work we solve thermo-hydrodynamical equations considering a two\ndimensional electron system in the integer quantum Hall regime, to calculate\nthe spatial distribution of the local electron temperature. We start from the\nself-consistently calculated electrostatic and electrochemical potentials in\nequilibrium. Next, by imposing an external current, we investigate the\nvariations of the electron temperature in the linear-response regime. Here a\nlocal relation between the electron density and conductivity tensor elements is\nassumed. Following the Ohm's law we obtain local current densities and by\nimplementing the results of the thermo-hydrodynamical theory, calculate the\nlocal electron temperature. We observe that the local electron temperature\nstrongly depends on the formation of compressible and incompressible strips.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Time scales for Majorana manipulation using Coulomb blockade in\n  gate-controlled superconducting nanowires: We numerically compute the low-energy spectrum of a gate-controlled\nsuperconducting topological nanowire segmented into two islands, each\nJosephson-coupled to a bulk superconductor. This device may host two pairs of\nMajorana bound states and could provide a platform for testing Majorana fusion\nrules. We analyze the crossover between (i) a charge-dominated regime\nutilizable for initialization and readout of Majorana bound states, (ii) a\nsingle-island regime for dominating inter-island Majorana coupling, (iii) a\nJosephson-plasmon regime for large coupling to the bulk superconductors, and\n(iv) a regime of four Majorana bound states allowing for topologically\nprotected Majorana manipulations. From the energy spectrum, we derive\nconservative estimates for the time scales of a fusion-rule testing protocol\nproposed recently [arXiv:1511.05153]. We also analyze the steps needed for\nbasic Majorana braiding operations in branched nanowire structures.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cooling of suspended nanostructures with tunnel junctions: We have investigated electronic cooling of suspended nanowires with SINIS\ntunnel junction coolers. The suspended samples consist of a free standing\nnanowire suspended by four narrow ($\\sim$ 200 nm) bridges. We have compared two\ndifferent cooler designs for cooling the suspended nanowire. We demonstrate\nthat cooling of the nanowire is possible with a proper SINIS cooler design.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous levitation and annihilation in Floquet topological insulators: Anderson localization in two-dimensional topological insulators takes place\nvia the so-called levitation and pair annihilation process. As disorder is\nincreased, extended bulk states carrying opposite topological invariants move\ntowards each other in energy, reducing the size of the topological gap,\neventually meeting and localizing. This results in a topologically trivial\nAnderson insulator. Here, we introduce the anomalous levitation and pair\nannihilation, a process unique to periodically-driven, or Floquet systems. Due\nto the periodicity of the quasienergy spectrum, we find it is possible for the\ntopological gap to increase as a function of disorder strength. Thus, after all\nbulk states have localized, the system remains topologically nontrivial,\nforming an anomalous Floquet Anderson insulator (AFAI) phase. We show a\nconcrete example for this process, adding disorder via onsite potential \"kicks\"\nto a Chern insulator model. By changing the period between kicks, we can tune\nwhich type of (conventional or anomalous) levitation-and-annihilation occurs in\nthe system. We expect our results to be applicable to generic Floquet\ntopological systems and to provide an accessible way to realize AFAIs\nexperimentally, without the need for multi-step driving schemes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin Polarization and Transport of Surface States in the Topological\n  Insulators Bi2Se3 and Bi2Te3 from First Principles: We investigate the band dispersion and the spin texture of topologically\nprotected surface states in the bulk topological insulators Bi2Se3 and Bi2Te3\nby first-principles methods. Strong spin-orbit entanglement in these materials\nreduces the spin-polarization of the surface states to ~50% in both cases; this\nreduction is absent in simple models but of important implications to\nessentially any spintronic application. We propose a way of controlling the\nmagnitude of spin polarization associated with a charge current in thin films\nof topological insulators by means of an external electric field. The proposed\ndual-gate device configuration provides new possibilities for electrical\ncontrol of spin.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Few-layer graphene patterned bottom gates for van der Waals\n  heterostructures: We introduce a method of local gating for van der Waals heterostructures,\nemploying a few-layer graphene patterned bottom gate. Being a member of the 2D\nmaterial family, few-layer graphene adapts perfectly to the commonly used\nstacking method. Its versatility regarding patterning as well as its flatness\nmake it an ideal candidate for experiments on locally gated 2D materials.\nMoreover, in combination with ultra-thin hexagonal boron nitride as an\ninsulating layer, sharp potential steps can be created and the quality of the\ninvestigated 2D material can be sustained. To underline the good feasibility\nand performance, we show results on transport experiments in periodically\nmodulated graphene- boron nitride heterostructures, where the charge carrier\ndensity is tuned via locally acting patterned few layer graphene bottom gates\nand a global back gate.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interplay of quantum spin Hall effect and spontaneous time-reversal\n  symmetry breaking in electron-hole bilayers I: Transport properties: The band-inverted electron-hole bilayers, such as InAs/GaSb, are an\ninteresting playground for the interplay of quantum spin Hall effect and\ncorrelation effects because of the small density of electrons and holes and the\nrelatively small hybridization between the electron and hole bands. It has been\nproposed that Coulomb interactions lead to a time-reversal symmetry broken\nphase when the electron and hole densities are tuned from the trivial to the\nquantum spin Hall insulator regime. We show that the transport properties of\nthe system in the time-reversal symmetry broken phase are consistent with the\nrecent experimental observations in InAs/GaSb. Moreover, we carry out a quantum\ntransport study on a Corbino disc where the bulk and edge contributions to the\nconductance can be separated. We show that the edge becomes smoothly conducting\nand the bulk is always insulating when one tunes the system from the trivial to\nthe quantum spin Hall insulator phase, providing unambiguous transport\nsignatures of the time-reversal symmetry broken phase.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Deviation from the normal mode expansion in a coupled\n  graphene-nanomechanical system: We optomechanically measure the vibrations of a nanomechanical system made of\na graphene membrane suspended on a silicon nitride nanoresonator. When probing\nthe thermal noise of the coupled nanomechanical device, we observe a\nsignificant deviation from the normal mode expansion. It originates from the\nheterogeneous character of mechanical dissipation over the spatial extension of\ncoupled eigenmodes, which violates one of the fundamental prerequisite for\nemploying this commonly used description of the nanoresonators' thermal noise.\nWe subsequently measure the local mechanical susceptibility and demonstrate\nthat the fluctuation-dissipation theorem still holds and permits a proper\nevaluation of the thermal noise of the nanomechanical system. Since it\nnaturally becomes delicate to ensure a good spatial homogeneity at the\nnanoscale, this approach is fundamental to correctly describe the thermal noise\nof nanomechanical systems which ultimately impact their sensing capacity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport properties of overheated electrons trapped on a Helium surface: An ultra-strong photovoltaic effect has recently been reported for electrons\ntrapped on a liquid Helium surface under a microwave excitation tuned at\nintersubband resonance [D. Konstantinov et. al. : J. Phys. Soc. Jpn. 81, 093601\n(2012) ]. In this article, we analyze theoretically the redistribution of the\nelectron density induced by an overheating of the surface electrons under\nirradiation, and obtain quantitative predictions for the photocurrent\ndependence on the effective electron temperature and confinement voltages. We\nshow that the photo-current can change sign as a function of the parameters of\nthe electrostatic confinement potential on the surface, while the photocurrent\nmeasurements reported so far have been performed only at a fixed confinement\npotential. The experimental observation of this sign reversal could provide a\nreliable estimation of the electron effective temperature in this new out of\nequilibrium state. Finally, we have also considered the effect of the\ntemperature on the outcome of capacitive transport measurement techniques.\nThese investigations led us to develop, numerical and analytical methods for\nsolving the Poisson-Boltzmann equation in the limit of very low temperatures\nwhich could be useful for other systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dirac fermion quantization on graphene edges: Isospin-orbit coupling,\n  zero modes and spontaneous valley polarization: The paper addresses boundary electronic properties of graphene with a complex\nedge structure of the armchair/zigzag/armchair type. It is shown that the\nfinite zigzag region supports edge bound states with discrete equidistant\nspectrum obtained from the Green's function of the continuum Dirac equation.\nThe energy levels exhibit the coupling between the valley degree of freedom and\nthe orbital quantum number, analogous to a spin-orbit interaction. The\ncharacteristic feature of the spectrum is the presence of a zero mode, the\nbound state of vanishing energy. It resides only in one of the graphene\nvalleys, breaking spontaneously Kramers' symmetry of the edge states. This\nimplies the spontaneous valley polarization characterized by the valley isospin\n$\\pm 1/2$. The polarization is manifested by a zero-magnetic field anomaly in\nthe local tunneling density of states, and is directly related to the local\nelectric Hall conductivity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strongly bound excitons in monolayer MoSi$_2$Z$_4$ (Z = pnictogen): Reduced dielectric screening in two-dimensional materials enables bound\nexcitons, which modifies their optical absorption and optoelectronic response\neven at room temperature. Here, we demonstrate the existence of excitons in the\nbandgap of the monolayer family of the newly discovered synthetic MoSi$_2$Z$_4$\n(Z = N, P, and As) series of materials. All three monolayers support several\nbright and strongly bound excitons with binding energies varying from 1 eV to\n1.35 eV for the lowest energy exciton resonances. On increasing the pump\nfluence, the exciton binding energies get renormalized, leading to a\nredshift-blueshift crossover. Our study shows that the MoSi$_2$Z$_4$ series of\nmonolayers offer an exciting test-bed for exploring the physics of strongly\nbound excitons and their non-equilibrium dynamics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Zero-field magnetometry using hyperfine-biased nitrogen-vacancy centers\n  near diamond surfaces: Shallow nitrogen-vacancy (NV) centers in diamond are promising for\nnano-magnetometry for they can be placed proximate to targets. To study the\nintrinsic magnetic properties, zero-field magnetometry is desirable. However,\nfor shallow NV centers under zero field, the strain near diamond surfaces would\ncause level anti-crossing between the spin states, leading to clock transitions\nwhose frequencies are insensitive to magnetic signals. Furthermore, the charge\nnoises from the surfaces would induce extra spin decoherence and hence reduce\nthe magnetic sensitivity. Here we demonstrate that the relatively strong\nhyperfine coupling (130 MHz) from a first-shell 13C nuclear spin can provide an\neffective bias field to an NV center spin so that the clock-transition\ncondition is broken and the charge noises are suppressed. The hyperfine bias\nenhances the dc magnetic sensitivity by a factor of 22 in our setup. With the\ncharge noises suppressed by the strong hyperfine field, the ac magnetometry\nunder zero field also reaches the limit set by decoherence due to the nuclear\nspin bath. In addition, the 130 MHz splitting of the NV center spin transitions\nallows relaxometry of magnetic noises simultaneously at two well-separated\nfrequencies (~2.870 +/- 0.065 GHz), providing (low-resolution) spectral\ninformation of high-frequency noises under zero field. The hyperfine-bias\nenhanced zero-field magnetometry can be combined with dynamical decoupling to\nenhance single-molecule magnetic resonance spectroscopy and to improve the\nfrequency resolution in nanoscale magnetic resonance imaging.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Nonlinear dynamics of a functionally graded piezoelectric\n  micro-resonator in the vicinity of the primary resonance: This research is on the nonlinear dynamics of a two-sided electrostatically\nactuated capacitive micro-beam. The microresonator is composed of silicon and\nPZT as a piezoelectric material. PZT is functionally distributed along the\nheight of the micro-beam according to the power law distribution. The\nmicro-resonator is simultaneously subjected to DC piezoelectric and two-sided\nelectrostatic actuations. The DC piezoelectric actuation leads to the\ngeneration of an axial force along the length of the micro-beam and this is\nused as a tuning tool to shift the primary resonance of the micro-resonator.\nThe governing equation of the motion is derived by the minimization of the\nHamiltonian and generalized to the viscously damped systems. The periodic\nsolutions in the vicinity of the primary resonance are detected by means of the\nshooting method and their stability is investigated by determining the\nso-called Floquet exponents of the perturbed motions. The basins of attraction\ncorresponding to three individual periodic orbits are determined. The results\ndepict that the higher the amplitude of the periodic orbit, the smaller is the\narea of the attractor",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Multiple Andreev reflections in a quantum dot coupled to\n  superconductors: Effects of spin-orbit coupling: We study the out-of-equilibrium current through a multilevel quantum dot\ncontacted to two superconducting leads and in the presence of Rashba and\nDresselhaus spin-orbit couplings, in the regime of strong dot-lead coupling.\nThe multiple Andreev reflection (MAR) subgap peaks in the current voltage\ncharacteristics are found to be modified (but not suppressed) by the spin-orbit\ninteraction, in a way that strongly depends on the shape of the dot confining\npotential. In a perfectly isotropic dot the MAR peaks are enhanced when the\nstrength $\\alpha_R$ and $\\alpha_D$ of Rashba and Dresselhaus terms are equal.\nWhen the anisotropy of the dot confining potential increases the dependence of\nthe subgap structure on the spin-orbit angle\n$\\theta=\\arctan(\\alpha_D/\\alpha_R)$ decreases. Furthermore, when an in-plane\nmagnetic field is applied to a strongly anisotropic dot, the peaks of the\nnon-linear conductance oscillate as a function of the magnetic field angle, and\nthe location of the maxima and minima allows for a straightforward read-out of\nthe spin-orbit angle $\\theta$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Emergence of a negative charging energy in a metallic dot capacitively\n  coupled to a superconducting island: We consider the hybrid setup formed by a metallic dot, capacitively coupled\nto a superconducting island S connected to a bulk superconductor by a Josephson\njunction. Charge fluctuations in S act as a dynamical gate and overscreen the\nelectronic repulsion in the metallic dot, producing an attractive interaction\nbetween two additional electrons. As the offset charge of the metallic dot is\nincreased, the dot charging curve shows positive steps ($+2e$) followed by\nnegative ones ($-e$) signaling the occurrence of a negative differential\ncapacitance. A proposal for experimental detection is given, and potential\napplications in nanoelectronics are mentioned.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spectral signatures of high-symmetry quantum dots and effects of\n  symmetry breaking: A sequence of photoluminescence spectroscopy based methods are used to\nrigorously identify and study all the main spectral features (more than thirty\nemission lines) of site controlled InGaAs/AlGaAs quantum dots (QDs) grown along\n[111]B in inverted tetrahedral pyramids. The studied QDs reveal signatures of\none confined electron level, one heavy-hole-like level and one light-hole-like\nlevel. The various heavy-light-hole hybrid exciton complexes formed in these\nQDs are studied by polarization resolved spectroscopy, excitation power\ndependence, crystal temperature dependence and temporal single photon\ncorrelation measurements. The presented approach, which only requires a minimal\ntheoretical input, enables strict spectral identification of the fine structure\npatterns including weak and spectrally overlapping emission lines. Furthermore,\nit allows the involved electron-hole and hole-hole exchange interaction\nenergies to be deduced from measurements. Intricate fine structure patterns are\nqualitatively understood by group theory and shown to be very sensitive to the\nexact symmetry of the QD. Emission patterns influenced by hole-hole exchange\ninteractions are found to be particularly useful for identifying QDs with high\n$C_{3v}$ symmetry and for probing symmetry breaking.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Floquet metal to insulator phase transitions in semiconductor nanowires: We study steady-states of semiconductor nanowires subjected to strong\nresonant time-periodic drives. The steady-states arise from the balance between\nelectron-phonon scattering, electron-hole recombination via photo-emission, and\nAuger scattering processes. We show that tuning the strength of the driving\nfield drives a transition between an electron-hole metal (EHM) phase and a\nFloquet insulator (FI) phase. We study the critical point controlling this\ntransition. The EHM-to-FI transition can be observed by monitoring the presence\nof peaks in the density-density response function which are associated with the\nFermi momentum of the EHM phase, and are absent in the FI phase. Our results\nmay help guide future studies towards inducing novel non-equilibrium phases of\nmatter by periodic driving.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interaction of a graphene sheet with a ferromagnetic metal plate: Nanoscale surface forces such as Casimir and the van der Waals forces can\nhave a significant influence on fabrication, handling and assembly processes as\nwell as the performance of micro and nano devices. In this paper, the\ninvestigation and the calculation of the Casimir force between a graphene sheet\nand a ferromagnetic metal substrate in a vacuum are presented. The reflection\ncoefficients of graphene are graphene-conductivity dependent, and the\nconductivity of graphene is described by the Kubo formalism. There is an effect\nof magnetic properties of the metal on the Casimir interaction. The magnetic\neffect plays a significant role at low temperatures or high value of chemical\npotential. The numerical results also demonstrate that the thickness of a metal\nslab has a minor influence on the Casimir force. The investigation and findings\nabout the Casimir force in this study would lead to useful information and\neffective solutions for design and manufacturing of micro and nano devices,\nespecially in the areas of micro and nano machining, fabrication, manipulation,\nassembly and metrology.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bright-exciton fine structures splittings in single perovskite\n  nanocrystals: Although both epitaxial quantum dots (QDs) and colloidal nanocrystals (NCs)\nare quantum-confined semiconductor nanostructures, so far they have\ndemonstrated dramatically-different exciton fine structure splittings (FSSs) at\nthe cryogenic temperature. The single-QD photoluminescence (PL) is dominated by\nthe bright-exciton FSS, while it is the energy separation between bright and\ndark excitons that is often referred to as the FSS in a single NC. Here we show\nthat, in single perovskite CsPbI3 NCs synthesized from a colloidal approach, a\nbright-exciton FSS as large as hundreds of {\\mu}eV can be resolved with two\northogonally- and linearly-polarized PL peaks. This PL doublet could switch to\na single peak when a single CsPbI3 NC is photo-charged to eliminate the\nelectron-hole exchange interaction. The above findings have prepared an\nefficient platform suitable for probing exciton and spin dynamics of\nsemiconductor nanostructures at the visible-wavelength range, from which a\nvariety of practical applications such as in entangled photon-pair source and\nquantum information processing can be envisioned.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Determination of the thickness and orientation of few-layer tungsten\n  ditelluride using polarized Raman spectroscopy: Orthorhombic tungsten ditelluride (WTe2), with a distorted 1T structure,\nexhibits a large magnetoresistance that depends on the orientation, and its\nelectrical characteristics changes rom semimetallic to insulating as the\nthickness decreases. Through polarized Raman spectroscopy in combination with\ntransmission electron diffraction, we establish a reliable method to determine\nthe thickness and crystallographic orientation of few-layer WTe2. The Raman\nspectrum shows a pronounced dependence on the polarization of the excitation\nlaser. We found that the separation between two Raman peaks at ~90 cm-1 and at\n80-86 cm-1, depending on thickness, is a reliable fingerprint for determination\nof the thickness. For determination of the crystallographic orientation, the\npolarization dependence of the A1 modes, measured with the 632.8-nm excitation,\nturns out to be the most reliable. We also discovered that the polarization\nbehaviors of some of the Raman peaks depend on the excitation wavelength as\nwell as thickness, indicating a close interplay between the band structure and\nanisotropic Raman scattering cross section.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Controlled strong coupling and absence of dark polaritons in\n  microcavities with double quantum wells: We demonstrate an efficient switching between strong and weak exciton-photon\ncoupling regimes in microcavity-embedded asymmetric double quantum wells,\ncontrolled by an applied electric field. We show that a fine tuning of the\nelectric field leads to drastic changes in the polariton properties, with the\npolariton ground state being red-shifted by a few meV and having acquired\nprominent features of a spatially indirect dipolar exciton. We study the\nproperties of dipolar exciton polaritons, called dipolaritons, on a microscopic\nlevel and show that, unlike recent findings, they are not dark polaritons but,\nowing to the finite size of the excition, are mixed states with comparable\ncontribution of the cavity photon, bright direct, and long-living indirect\nexciton modes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Transport in Spin-1 Chiral Fermion: Self-Consistent Born\n  Approximation: Quantum transport for a spin-1 chiral fermion is studied within the\nself-consistent Born approximation. We find characteristic properties around\nzero energy, i.e., the peak structure of the density of states and significant\nsuppression of electrical conductivity. These structures originate from the\nflat band and its interband effect.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Velocity shift of surface acoustic waves due to interaction with\n  composite fermions in a modulated structure: We study the effect of a periodic density modulation on surface acoustic wave\n(SAW) propagation along a 2D electron gas near Landau level filling $\\nu=1/2$.\nWithin the composite fermion theory, the problem is described in terms of\nfermions subject to a spatially modulated magnetic field and scattered by a\nrandom magnetic field. We find that a few percent modulation induces a large\npeak in the SAW velocity shift, as has been observed recently by Willett et al.\nAs further support of this theory we find the dc resistivity to be in good\nagreement with recent data of Smet et al.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunnel Barrier to Spin Filter: Electronic Transport Characteristics of\n  Transition Metal Atom Encapsulated in Smallest Cadmium Telluride Cage: We report first principles theory-based comparative electronic transport\nstudies performed for an atomic chain of Au, bare Cd9Te9 cage-like cluster and\nsingle transition metal (TM) (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd)\natom encapsulated within the Cd9Te9 using Au(111) as electrodes. The bare\ncluster is semiconducting and acts as a tunnel barrier up to a particular\napplied bias and beyond that, the device has a linear current-voltage\nrelationship. Several TM (Ti, V, Cr, Mn, Fe) encapsulated in the cage show\nhalf-metallic behavior and spin filtering effect in the I-V characteristics of\nthe device. A detailed qualitative and quantitative analysis of I-V\ncharacteristics for metallic, semiconducting, and half-metallic nanostructures\nhas been carried out.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Antiunitary symmetry protected higher order topological phases: Higher-order topological (HOT) phases feature boundary (such as corner and\nhinge) modes of codimension $d_c>1$. We here identify an \\emph{antiunitary}\noperator that ensures the spectral symmetry of a two-dimensional HOT insulator\nand the existence of cornered localized states ($d_c=2$) at precise zero\nenergy. Such an antiunitary symmetry allows us to construct a generalized HOT\ninsulator that continues to host corner modes even in the presence of a\n\\emph{weak} anomalous Hall insulator and a spin-orbital density wave orderings,\nand is characterized by a quantized quadrupolar moment $Q_{xy}=0.5$. Similar\nconclusions can be drawn for the time-reversal symmetry breaking HOT $p+id$\nsuperconductor and the corner localized Majorana zero modes survive even in the\npresence of weak Zeeman coupling and $s$-wave pairing. Such HOT insulators also\nserve as the building blocks of three-dimensional second-order Weyl semimetals,\nsupporting one-dimensional hinge modes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron spin tomography through counting statistics: a quantum\n  trajectory approach: We investigate the dynamics of electron spin qubits in quantum dots.\nMeasurement of the qubit state is realized by a charge current through the dot.\nThe dynamics is described in the framework of the quantum trajectory approach,\nwidely used in quantum optics, and we show that it can be applied successfully\nto problems in condensed matter physics. The relevant master equation dynamics\nis unravelled to simulate stochastic tunneling events of the current through\nthe dot.Quantum trajectories are then used to extract the counting statistics\nof the current. We show how, in combination with an electron spin resonance\n(ESR) field, counting statistics can be employed for quantum state tomography\nof the qubit state. Further, it is shown how decoherence and relaxation time\nscales can be estimated with the help of counting statistics, in the time\ndomain. Finally, we discuss a setup for single shot measurement of the qubit\nstate without the need for spin-polarized leads.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "High Frequency Response of Volatile Memristors: In this theoretical study, we focus on the high-frequency response of the\nelectrothermal NbO2-Mott threshold switch, a real-world electronic device,\nwhich has been proved to be relevant in several applications and is classified\nas a volatile memristor. Memristors of this kind, have been shown to exhibit\ndistinctive non-linear behaviors crucial for cutting-edge neuromorphic\ncircuits. In accordance with well-established models for these devices, their\nresistances depend on their body temperatures, which evolve over time following\nNewton's Law of Cooling. Here, we demonstrate that HP's NbO2-Mott memristor can\nmanifest up to three distinct steady-state oscillatory behaviors under a\nsuitable high-frequency periodic voltage input, showcasing increased\nversatility despite its volatile nature. Additionally, when subjected to a\nhigh-frequency periodic voltage signal, the device body temperature oscillates\nwith a negligible peak-to-peak amplitude. Since, the temperature remains almost\nconstant over an input cycle, the devices under study behave as linear\nresistors during each input cycle. Based on these insights, this paper presents\nanalytical equations characterizing the response of the NbO2-Mott memristor to\nhigh-frequency voltage inputs, demarcating regions in the state space where\ndistinct initial conditions lead to various asymptotic oscillatory behaviors.\nImportantly, the mathematical methods introduced in this manuscript are\napplicable to any volatile electrothermal resistive switch. Additionally, this\npaper presents analytical equations that accurately reproduce the temperature\ntime-waveform of the studied device during both its transient and steady-state\nphases when subjected to a zero-mean sinusoidal voltage input oscillating in\nthe high-frequency limit.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Double quantum dot as a probe of nonequilibrium charge fluctuations at\n  the quantum point contact: Absorption of energy quanta generated by quantum point contact results in the\ninelastic current through the double quantum dot placed nearby. In contrast to\na single quantum dot, the inelastic current through the double quantum dot is\nsensitive to the energy dependence of the quantum point contact transmission,\nwhich can explain the experimentally observed features. We calculate the\ninelastic current as a function of microscopic parameters of the circuit.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Phonon-dressed Mollow triplet in the regime of cavity-QED: We study the resonance fluorescence spectra of a driven quantum dot placed\ninside a high $Q$ semiconductor cavity and interacting with an acoustic phonon\nbath. The dynamics is calculated using a time-convolutionless master equation\nobtained in the polaron frame. We demonstrate pronounced spectral broadening of\nthe Mollow sidebands through cavity-emission which, for small cavity-coupling\nrates, increases quadratically with the Rabi frequency. However, for larger\ncavity coupling rates, this broadening dependence is found to be more complex.\nThis field-dependent Mollow triplet broadening is primarily a consequence of\nthe triplet peaks sampling different parts of the asymmetric phonon bath, and\nagrees directly with recent experiments with semiconductor micropillars. The\ninfluence from the detuned cavity photon bath and multi-photon effects is shown\nto play a qualitatively important role on the fluorescence spectra.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effect of van-Hove singularities in single-walled carbon nanotube leads\n  on transport through double quantum dot system: The double quantum dot system with single-walled metallic armchair carbon\nnanotube leads has been studied using Non-equilibrium Green function in the\nKeldysh formalism. The effect of relative spacing between the energy levels of\nthe dots, interdot tunneling matrix-element, interdot Coulomb interaction and\nvan-Hove singularities in density of states characteristics of\nquasi-one-dimensional carbon nanotube leads on the conductance of the double\nquantum dot system has been studied. The conductance and dot occupancies are\ncalculated at finite temperature. It is observed that the density of states of\nthe carbon nanotube leads play a significant role in determining the\nconductance profile. In particular, whenever the chemical potential of the\nisolated double quantum dot system is aligned with the position of a van-Hove\nsingularity in the density of states of armchair carbon nanotube leads, the\nheight of the corresponding conductance peak falls considerably. It is further\nobserved that the suppression in the heights of the alternate peaks depends on\nthe relative positions of the energy levels of the dots and their magnitude of\nseparation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Models of Electrodes and Contacts in Molecular Electronics: Bridging the difference in atomic structure between experiments and\ntheoretical calculations and exploring quantum confinement effects in thin\nelectrodes (leads) are both important issues in molecular electronics. To\naddress these issues, we report here, by using Au-benzenedithiol-Au as a model\nsystem, systematic investigations of different models for the leads and the\nlead-molecule contacts: leads with different cross-sections, leads consisting\nof infinite surfaces, and surface leads with a local nanowire or atomic chain\nof different lengths. The method adopted is a non-equilibrium Green function\napproach combined with density functional theory calculations for the\nelectronic structure and transport, in which the leads and molecule are treated\non the same footing. It is shown that leads with a small cross-section will\nlead to large oscillations in the transmission function, T(E), which depend\nsignificantly on the lead structure (orientation) because of quantum waveguide\neffects. This oscillation slowly decays as the lead width increases, with the\naverage approaching the limit given by infinite surface leads. Local nanowire\nstructures around the contacts induce moderate fluctuations in T(E), while a Au\natomic chain (including a single Au apex atom) at each contact leads to a\nsignificant conductance resonance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Efficient electrical spin readout of NV- centers in diamond: Using pulsed photoionization the coherent spin manipulation and echo\nformation of ensembles of NV- centers in diamond are detected electrically\nrealizing contrasts of up to 17 %. The underlying spin-dependent ionization\ndynamics are investigated experimentally and compared to Monte-Carlo\nsimulations. This allows the identification of the conditions optimizing\ncontrast and sensitivity which compare favorably with respect to optical\ndetection.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Large Landau level splitting with tunable one-dimensional graphene\n  superlattice probed by magneto capacitance measurements: The unique zero energy Landau Level of graphene has a particle-hole symmetry\nin the bulk, which is lifted at the boundary leading to a splitting into two\nchiral edge modes. It has long been theoretically predicted that the splitting\nof the zero-energy Landau level inside the {\\it bulk} can lead to many\ninteresting physics, such as quantum spin Hall effect, Dirac like singular\npoints of the chiral edge modes, and others. However, so far the obtained\nsplitting with high-magnetic field even on a hBN substrate are not amenable to\nexperimental detection, and functionality. Guided by theoretical calculations,\nhere we produce a large gap zero-energy Landau level splitting ($\\sim$ 150 meV)\nwith the usage of a one-dimensional (1D) superlattice potential. We have\ncreated tunable 1D superlattice in a hBN encapsulated graphene device using an\narray of metal gates with a period of $\\sim$ 100 nm. The Landau level spectrum\nis visualized by measuring magneto capacitance spectroscopy. We monitor the\nsplitting of the zeroth Landau level as a function of superlattice potential.\nThe observed splitting energy is an order higher in magnitude compared to the\nprevious studies of splitting due to the symmetry breaking in pristine\ngraphene. The origin of such large Landau level spitting in 1D potential is\nexplained with a degenerate perturbation theory. We find that owing to the\nperiodic potential, the Landau level becomes dispersive, and acquires sharp\npeaks at the tunable band edges. Our study will pave the way to create the\ntunable 1D periodic structure for multi-functionalization and device\napplication like graphene electronic circuits from appropriately engineered\nperiodic patterns in near future.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Comment on \"Do Intradot Electron-Electron Interactions Induce\n  Dephasing?\": In a recent Letter, Jiang, Sun, Xie and Wang [Phys. Rev. Lett. 93, 076802\n(2004), cond-mat/0408261] study transport through an interacting quantum dot\nembedded in one arm of an Aharonov-Bohm interferometer. Based on a theoretical\nanalysis of the Aharonov-Bohm oscillation amplitude, Jiang {\\it et al.} claim,\ncontrary to earlier work by two of us, that at finite temperature the intradot\ninteraction will {\\em not} lead to any dephasing. Likewise, they claim that the\ntheoretically predicted and experimentally verified asymmetry of the\nAharonov-Bohm oscillation amplitude is {\\em not} associated with dephasing. In\nthis Comment, we point out severe inconsistencies in the analysis of the Letter\nby Jian {\\it et al.}, and show that their conclusions are ill-founded.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin noise of localized electrons interacting with optically cooled\n  nuclei: A microscopic theory of spin fluctuations of localized electrons interacting\nwith optically cooled nuclear spin bath has been developed. Since nuclear spin\ntemperature may stay low enough for macroscopically long time, the nuclear spin\nsystem becomes very sensitive to an external magnetic field. This strongly\naffects electron spin noise spectrum. It has been shown that in the case of\nweak fields/relatively high nuclear spin temperature, a small degree of nuclear\nspin polarization affect the electron spin fluctuations in the same way as an\nadditional external magnetic field. By contrast, the high degree of nuclear\npolarization realized in relatively strong magnetic field and low nuclear spin\ntemperature leads to a suppression of hyperfine field fluctuations and to a\ndramatic narrowing of precession-induced peak in the spin noise spectrum. The\nexperimental possibilities of nuclear spin system investigation by means of\nspin noise spectroscopy are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strain engineering of the electronic states of silicon-based quantum\n  emitters: Light-emitting complex defects in silicon have been considered a potential\nplatform for quantum technologies based on spin and photon degrees of freedom\nworking at telecom wavelengths. Their integration in complex devices is still\nin its infancy, and it was mostly focused on light extraction and guiding. Here\nwe address the control of the electronic states of carbon-related impurities\n(G-centers) via strain engineering. By embedding them in patches of silicon on\ninsulator and topping them with SiN, symmetry breaking along [001] and [110]\ndirections is demonstrated, resulting in a controlled splitting of the zero\nphonon line (ZPL), as accounted for by the piezospectroscopic theoretical\nframework. The splitting can be as large as 18 meV and it is finely tuned by\nselecting patch size or by moving in different positions on the patch. Some of\nthe split, strained ZPLs are almost fully polarized and their overall intensity\nis enhanced up to 7 times with respect to the flat areas, whereas their\nrecombination dynamics is slightly affected. Our technique can be extended to\nother impurities and Si-based devices such as suspended bridges, photonic\ncrystal microcavities, Mie resonators, and integrated photonic circuits.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical Phonons in Twisted Bilayer Graphene with Gate-Induced Asymmetric\n  Doping: Twisted bilayer graphene (tBLG) devices with ion gel gate dielectrics are\nstudied using Raman spectroscopy in the twist angle regime where a resonantly\nenhanced G band can be observed. We observe prominent splitting and intensity\nquenching on the G Raman band when the carrier density is tuned away from\ncharge neutrality. This G peak splitting is attributed to asymmetric charge\ndoping in the two graphene layers, which reveals individual phonon self-energy\nrenormalization of the two weakly-coupled layers of graphene. We estimate the\neffective interlayer capacitance at low doping density of tBLG using an\ninterlayer screening model. The anomalous intensity quenching of both G peaks\nis ascribed to the suppression of resonant interband transitions between the\ntwo saddle points (van Hove singularities), that are displaced in the momentum\nspace by gate-tuning. In addition, we observe a softening (hardening) of the R\nRaman band, a superlattice-induced phonon mode in tBLG, in electron (hole)\ndoping. Our results demonstrate that gate modulation can be used to control the\noptoelectronic and vibrational properties in tBLG devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Distribution of waiting times between electron cotunnelings: In the resonant tunneling regime sequential processes dominate single\nelectron transport through quantum dots or molecules that are weakly coupled to\nmacroscopic electrodes. In the Coulomb blockade regime, however, cotunneling\nprocesses dominate. Cotunneling is an inherently quantum phenomenon and thus\ngives rise to interesting observations, such as an increase in the current shot\nnoise. Since cotunneling processes are inherently fast compared to the\nsequential processes, it is of interest to examine the short time behaviour of\nsystems where cotunneling plays a role, and whether these systems display\nnonrenewal statistics. We consider three questions in this paper. Given that an\nelectron has tunneled from the source to the drain via a cotunneling or\nsequential process, what is the waiting time until another electron cotunnels\nfrom the source to the drain? What are the statistical properties of these\nwaiting time intervals? How does cotunneling affect the statistical properties\nof a system with strong inelastic electron-electron interactions? In answering\nthese questions, we extend the existing formalism for waiting time\ndistributions in single electron transport to include cotunneling processes via\nan $n$-resolved Markovian master equation. We demonstrate that for a single\nresonant level the analytic waiting time distribution including cotunneling\nprocesses yields information on individual tunneling amplitudes. For both a SRL\nand an Anderson impurity deep in the Coulomb blockade there is a nonzero\nprobability for two electrons to cotunnel to the drain with zero waiting time\ninbetween. Furthermore, we show that at high voltages cotunneling processes\nslightly modify the nonrenewal behaviour of an Anderson impurity with a strong\ninelastic electron-electron interaction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bound states in the continuum in a two-channel Fano-Anderson model: In this article, we study the formation of the bound states in the continuum\n(BICs) in a two-channel Fano-Anderson model. We employ the Green's function\nformalism, together with the equation of motion method, to analyze the relevant\nobservables, such as the transmission coefficient and the density of states.\nMost importantly, our results show that the system hosts true BICs for the case\nof a symmetric configuration with the degenerate impurity levels, and a\ncomplete transmission channel is then suppressed. Finally, we argue that the\nproposed mechanism could be relevant for the realization of BICs in the\nelectronic and photonic systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetization reversal in Py/Gd heterostructures: Using a combination of magnetometry and magnetotransport techniques, we\nstudied temperature and magnetic field behavior of magnetization in Py/Gd\nheterostructures. It was shown quantitatively that proximity with Py enhances\nmagnetic order of Gd. Micromagnetic simulations demonstrate that a spin-flop\ntransition observed in a Py/Gd bilayer is due to exchange-spring rotation of\nmagnetization in the Gd layer. Transport measurements show that the\nmagnetoresistance of a [Py(2 nm)/Gd(2 nm)]25 multilayer changes sign at the\ncompensation temperature and below 20 K. The positive magnetoresistance above\nthe compensation temperature can be attributed to an in-plane domain-wall,\nwhich appears because of the structural inhomogeneity of the film over its\nthickness. By measuring the angular dependence of resistance we are able to\ndetermine the angle between magnetizations in the multilayer and the magnetic\nfield at different temperatures. The measurement reveals that due to a change\nof the chemical thickness profile, a non-collinear magnetization configuration\nis only stable in magnetic fields above 10 kOe.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Waveguide-integrated single-crystalline GaP resonators on diamond: Large-scale entanglement of nitrogen-vacancy (NV) centers in diamond will\nrequire integration of NV centers with optical networks. Toward this goal, we\npresent the fabrication of single-crystalline gallium phosphide (GaP)\nresonator-waveguide coupled structures on diamond. We demonstrate coupling\nbetween 1 {\\mu}m diameter GaP disk resonators and waveguides with a loaded Q\nfactor of 3,800, and evaluate their potential for efficient photon collection\nif integrated with single photon emitters. This work opens a path toward\nscalable NV entanglement in the hybrid GaP/diamond platform, with the potential\nto integrate on-chip photon collection, switching, and detection for\napplications in quantum information processing.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spectroscopy and level detuning of few-electron spin states in parallel\n  InAs quantum dots: We use tunneling spectroscopy to study the evolution of few-electron spin\nstates in parallel InAs nanowire double quantum dots (QDs) as a function of\nlevel detuning and applied magnetic field. Compared to the much more studied\nserial configuration, parallel coupling of the QDs to source and drain greatly\nexpands the probing range of excited state transport. Owing to a strong\nconfinement, we can here isolate transport involving only the very first\ninteracting single QD orbital pair. For the (2,0)-(1,1) charge transition, with\nrelevance for spin-based qubits, we investigate the excited (1,1) triplet, and\nhybridization of the (2,0) and (1,1) singlets. An applied magnetic field splits\nthe (1,1) triplet, and due to spin-orbit induced mixing with the (2,0) singlet,\nwe clearly resolve transport through all triplet states near the avoided\nsinglet-triplet crossings. Transport calculations, based on a simple model with\none orbital on each QD, fully replicate the experimental data. Finally, we\nobserve an expected mirrored symmetry between the 1-2 and 2-3 electron\ntransitions resulting from the two-fold spin degeneracy of the orbitals.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum superposition of a single microwave photon in two different\n  \"colour\" states: The ability to coherently couple arbitrary harmonic oscillators in a\nfully-controlled way is an important tool to process quantum information.\nCoupling between quantum harmonic oscillators has previously been demonstrated\nin several physical systems by use of a two-level system as a mediating\nelement. Direct interaction at the quantum level has only recently been\nrealized by use of resonant coupling between trapped ions. Here we implement a\ntunable direct coupling between the microwave harmonics of a superconducting\nresonator by use of parametric frequency conversion. We accomplish this by\ncoupling the mode currents of two harmonics through a superconducting quantum\ninterference device (SQUID) and modulating its flux at the difference (~ 7 GHz)\nof the harmonic frequencies. We deterministically prepare a single-photon Fock\nstate and coherently manipulate it between multiple modes, effectively\ncontrolling it in a superposition of two different \"colours\". This parametric\ninteraction can be described as a beam-splitter-like operation that couples\ndifferent frequency modes. As such, it could be used to implement linear\noptical quantum computing protocols on-chip.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coherent Radiation by Quantum Dots and Magnetic Nanoclusters: The assemblies of either quantum dots or magnetic nanoclusters are studied.\nIt is shown that such assemblies can produce coherent radiation. A method is\ndeveloped for solving the systems of nonlinear equations describing the\ndynamics of such assemblies. The method is shown to be general and applicable\nto systems of different physical nature. Despite mathematical similarities of\ndynamical equations, the physics of the processes for quantum dots and magnetic\nnanoclusters is rather different. In a quantum dot assembly, coherence develops\ndue to the Dicke effect of dot interactions through the common radiation field.\nFor a system of magnetic clusters, coherence in the spin motion appears due to\nthe Purcell effect caused by the feedback action of a resonator. Self-organized\ncoherent spin radiation cannot arise without a resonator. This principal\ndifference is connected with the different physical nature of dipole forces\nbetween the objects. Effective dipole interactions between the radiating\nquantum dots, appearing due to photon exchange, collectivize the dot radiation.\nWhile the dipolar spin interactions exist from the beginning, yet before\nradiation, and on the contrary, they dephase spin motion, thus destroying the\ncoherence of moving spins. In addition, quantum dot radiation exhibits\nturbulent photon filamentation that is absent for radiating spins.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Negative differential magneto-resistance in ferromagnetic wires with\n  domain walls: A domain wall in a ferromagnetic one-dimensional nanowire experiences current\ninduced motion due to its coupling with the conduction electrons. When the\ncurrent is not sufficient to drive the domain wall through the wire, or it is\nconfined to a perpendicular layer, it nonetheless experiences oscillatory\nmotion. In turn, this oscillatory motion of the domain wall can couple\nresonantly with the electrons in the system affecting the transport properties\nfurther. We investigate the effect of the coupling between these domain wall\nmodes and the current electrons on the transport properties of the system and\nshow that such a system demonstrates negative differential magnetoresistance\ndue to the resonant coupling with the low-lying modes of the domain wall\nmotion.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mu-Metal Enhancement of Effects in Electromagnetic Fields Over Single\n  Emitters Near Topological Insulators: We focus on the transmission and reflection coefficients of light in systems\ninvolving of topological insulators (TI). Due to the electro-magnetic coupling\nin TIs, new mixing coefficients emerge leading to new components of the\nelectromagnetic fields of propagating waves. We have discovered a simple\nheterostructure that provides a 100-fold enhancement of the mixing coefficients\nfor TI materials. Such effect increases with the TI's wave impedance. We also\npredict a transverse deviation of the Poynting vector due to these mixed\ncoefficients contributing to the radiative electromagnetic field of an electric\ndipole. Given an optimal configuration of the dipole-TI system, this deviation\ncould amount to $0.18\\%$ of the Poynting vector due to emission near not\ntopological materials, making this effect detectable.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ultrafast switchable spin-orbit coupling for silicon spin qubits via\n  spin valves: Recent experimental breakthroughs, particularly for single-qubit and\ntwo-qubit gates exceeding the error correction threshold, highlight silicon\nspin qubits as leading candidates for fault-tolerant quantum computation. In\nthe existing architecture, intrinsic or synthetic spin-orbit coupling (SOC) is\ncritical in various aspects, including electrical control, addressability,\nscalability, etc. However, the high-fidelity SWAP operation and quantum state\ntransfer (QST) between spin qubits, crucial for qubit-qubit connectivity,\nrequire the switchable nature of SOC which is rarely considered. Here, we\npropose a flexible architecture based on spin valves by electrically changing\nits magnetization orientation within sub-nanoseconds to generate ultrafast\nswitchable SOC. Based on the switchable SOC architecture, both SWAP operation\nof neighbor spin qubits and resonant QST between distant spins can be realized\nwith fidelity exceeding 99% while considering the realistic experimental\nparameters. Benefiting from the compatible processes with the modern\nsemiconductor industry and experimental advances in spin valves and spin\nqubits, our results pave the way for future construction of silicon-based\nquantum chips.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A semiclassical treatment of spinor topological effects in driven,\n  inhomogeneous insulators under external electromagnetic fields: Introducing internal degrees of freedom in the description of topological\ninsulators has led to a myriad of theoretical and experimental advances. Of\nparticular interest are the effects of periodic perturbations, either in time\nor space, as they considerably enrich the variety of electronic responses, with\nexamples such as Thouless's charge pump and its higher dimensional cousins, or,\nhigher-order topological insulators. Here, we develop a semiclassical approach\nto transport and accumulation of general spinor degrees of freedom, such as\nphysical spin, valley, or atomic orbits, in adiabatically driven, weakly\ninhomogeneous insulators of dimensions one, two and three under external\nelectromagnetic fields. Specifically, we focus on physical spins and derive the\nspin current and density up to third order in the spatio-temporal modulations\nof the system. We, then, relate these contributions to geometrical and\ntopological objects -- the spin-Chern fluxes and numbers -- defined over the\nhigher-dimensional phase-space of the system, i.e., its combined\nmomentum-position-time coordinates. Furthermore, we provide a connection\nbetween our semiclassical analysis and the modern theory of multipole moments\nby introducing spin analogues of the electric dipole, quadrupole and octapole\nmoments. The results are showcased in concrete tight-binding models where the\ninduced responses are calculated analytically.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum oscillations in two coupled charge qubits: Despite an apparent progress in implementing individual solid-state qubits,\nthere have been no experimental reports so far on multi-bit gates required for\nbuilding a real quantum computer. Here we report a new circuit comprising two\ncoupled charge qubits. Using a pulse technique, we coherently mix quantum\nstates and observe quantum oscillations whose spectrum reflects interaction\nbetween the qubits. Our results demonstrate the feasibility of coupling of\nmultiple solid-state qubits and indicate the existence of entangled two-qubit\nstates.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Shuttle in Phase Space: We present a quantum theory of the shuttle instability in electronic\ntransport through a nanostructure with a mechanical degree of freedom. A phase\nspace formulation in terms of the Wigner function allows us to identify a\ncross-over from the tunnelling to the shuttling regime, thus extending the\npreviously found classical results to the quantum domain. Further, a new\ndynamical regime is discovered, where the shuttling is driven exclusively by\nthe quantum noise.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Engineering single donor detectors in doped silicon: We demonstrate the possibility of engineering a single donor transistor\ndirectly from a phosphorous doped quantum dot by making use of the intrinsic\nglassy behaviour of the structure as well as the complex electron dynamics\nduring cooldown. Characterisation of the device at low temperatures and in\nmagnetic field shows single donors can be electrostatically isolated near one\nof the tunnel barrier with either a single or a doubly occupancy. Such a model\nis well supported by capacitance-based simulations. Ability of using the D0 of\nsuch isolated donor as a charge detector is demonstrated by observing the\ncharge stability diagram of a nearby and capacitively coupled semi-connected\ndouble quantum dot.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dielectric screening in two-dimensional insulators: Implications for\n  excitonic and impurity states in graphane: For atomic thin layer insulating materials we provide an exact analytic form\nof the two-dimensional screened potential. In contrast to three-dimensional\nsystems where the macroscopic screening can be described by a static dielectric\nconstant in 2D systems the macroscopic screening is non local (q-dependent)\nshowing a logarithmic divergence for small distances and reaching the\nunscreened Coulomb potential for large distances. The cross-over of these two\nregimes is dictated by 2D layer polarizability that can be easily computed by\nstandard first-principles techniques. The present results have strong\nimplications for describing gap-impurity levels and also exciton binding\nenergies. The simple model derived here captures the main physical effects and\nreproduces well, for the case of graphane, the full many-body GW plus\nBethe-Salpeter calculations. As an additional outcome we show that the impurity\nhole-doping in graphane leads to strongly localized states, what hampers\napplications in electronic devices. In spite of the inefficient and nonlocal\ntwo-dimensional macroscopic screening we demonstrate that a simple\n$\\mathbf{k}\\cdot\\mathbf{p}$ approach is capable to describe the electronic and\ntransport properties of confined 2D systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A topological look at the quantum spin Hall state: We propose a topological understanding of the quantum spin Hall state without\nconsidering any symmetries, and it follows from the gauge invariance that\neither the energy gap or the spin spectrum gap needs to close on the system\nedges, the former scenario generally resulting in counterpropagating gapless\nedge states. Based upon the Kane-Mele model with a uniform exchange field and a\nsublattice staggered confining potential near the sample boundaries, we\ndemonstrate the existence of such gapless edge states and their robust\nproperties in the presence of impurities. These gapless edge states are\nprotected by the band topology alone, rather than any symmetries.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coulomb scattering cross-section in a 2D electron gas and production of\n  entangled electrons: We calculate the Coulomb scattering amplitude for two electrons injected with\nopposite momenta in an interacting 2DEG. We include the effect of the Fermi\nliquid background by solving the 2D Bethe-Salpeter equation for the\ntwo-particle Green function vertex, in the ladder and random phase\napproximations. This result is used to discuss the feasibility of producing\nspin EPR pairs in a 2DEG by collecting electrons emerging from collisions at a\npi/2 scattering angle, where only the entangled spin-singlets avoid the\ndestructive interference resulting from quantum indistinguishability.\nFurthermore, we study the effective 2D electron-electron interaction due to the\nexchange of virtual acoustic and optical phonons, and compare it to the Coulomb\ninteraction. Finally, we show that the 2D Kohn-Luttinger pairing instability\nfor the scattering electrons is negligible in a GaAs 2DEG.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strong Band Hybridization between Silicene and Ag(111)Substrate: By using first-principles calculations, we systematically investigated\nseveral observed phases of silicene on Ag(111) substrates and their electronic\nstructures. We find that the original Dirac cone of silicene is about 1.5-1.7\neV deeply below the Fermi level and severely destroyed by the band\nhybridization between silicene and Ag in all the examined phases. Thus,\nsilicene synthesized on Ag(111) substrates could not preserve its excellent\nelectronic property and new method is needed to develop in synthesizing\nsilicene with its Dirac cone surviving.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fano-shaped impurity spectral density, electric-field-induced in-gap\n  state and local magnetic moment of an adatom on trilayer graphene: Recently, the existence of local magnetic moment in a hydrogen adatom on\ngraphene has been confirmed experimentally [Gonz\\'{a}lez-Herrero et al.,\nScience, 2016, 352, 437]. Inspired by this breakthrough, we theoretically\ninvestigate the top-site adatom on trilayer graphene (TLG) by solving the\nAnderson impurity model via self-consistent mean field method. The influence of\nthe stacking order, the adsorption site and external electric field are\ncarefully considered. We find that, due to its unique electronic structure, the\nsituation of the TLG is drastically different from that of the monolayer\ngraphene. Firstly, the adatom on rhombohedral stacked TLG (r-TLG) can have a\nFano-shaped impurity spectral density, instead of the normal Lorentzian-like\none, when the impurity level is around the Fermi level. Secondly, the impurity\nlevel of the adatom on r-TLG can be tuned into an in-gap state by an external\nelectric field, which strongly depends on the direction of the applied electric\nfield and can significantly affect the local magnetic moment formation.\nFinally, we systematically calculate the impurity magnetic phase diagrams,\nconsidering various stacking orders, adsorption sites, doping and electric\nfield. We show that, because of the in-gap state, the impurity magnetic phase\nof r-TLG will obviously depend on the direction of the applied electric field\nas well. All our theoretical results can be readily tested in experiment, and\nmay give a comprehensive understanding about the local magnetic moment of\nadatom on TLG.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transfer matrix solution of the Wako-Sait\u00f4-Mu\u00f1oz-Eaton model\n  augmented by arbitrary short range interactions: The Wako-Sait{\\^o}-Mu\\~noz-Eaton (WSME) model, initially introduced in the\ntheory of protein folding, has also been used in modeling the RNA folding and\nsome epitaxial phenomena. The advantage of this model is that it admits exact\nsolution in the general inhomogeneous case (Bruscolini and Pelizzola, 2002)\nwhich facilitates the study of realistic systems. However, a shortcoming of the\nmodel is that it accounts only for interactions within continuous stretches of\nnative bonds or atomic chains while neglecting interstretch (interchain)\ninteractions. But due to the biopolymer (atomic chain) flexibility, the\nmonomers (atoms) separated by several non-native bonds along the sequence can\nbecome closely spaced. This produces their strong interaction. The inclusion of\nnon-WSME interactions into the model makes the model more realistic and\nimproves its performance. In this study we add arbitrary interactions of finite\nrange and solve the new model by means of the transfer matrix technique. We can\ntherefore exactly account for the interactions which in proteomics are\nclassified as medium- and moderately long-range ones.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A spin dephasing mechanism mediated by the interplay between the\n  spin-orbit coupling and the asymmetrical confining potential in semiconductor\n  quantum dot: Understanding the spin dephasing mechanism is of fundamental importance in\nall potential applications of the spin qubit. Here we demonstrate a spin\ndephasing mechanism in semiconductor quantum dot due to the $1/f$ charge noise.\nThe spin-charge interaction is mediated by the interplay between the spin-orbit\ncoupling and the asymmetrical quantum dot confining potential. The dephasing\nrate is proportional to both the strength of the spin-orbit coupling and the\ndegree of the asymmetry of the confining potential. For parameters typical of\nthe InSb, InAs, and GaAs quantum dots with a moderate well-height $V_{0}=10$\nmeV, we find the spin dephasing times are ${\\rm T}^{*}_{2}=7$ $\\mu$s, $275$\n$\\mu$s, and $55$ ms, respectively. In particular, the spin dephasing can be\nenhanced by lowering the well-height. When the well-height is as small as\n$V_{0}=5$ meV, the spin depahsing times in the InSb, InAs, and GaAs quantum\ndots are decreased to ${\\rm T}^{*}_{2}=0.38$ $\\mu$s, $18$ $\\mu$s, and $9$ ms,\nrespectively.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Origin of thermoelectric response fluctuations in single-molecule\n  junctions: The thermoelectric response of molecular junctions exhibits large\nfluctuations, as observed in recent experiments [e.g. Malen J. A. {\\sl et al.},\nNano Lett. {\\bf 10}, 3406 (2009)]. These were attributed to fluctuations in the\nenergy alignment between the highest occupied molecular orbital (HOMO) and the\nFermi level at the electrodes. By analyzing these fluctuations assuming\nresonant transport through the HOMO level, we demonstrate that fluctuations in\nthe HOMO level alone cannot account for the observed fluctuations in the\nthermopower, and that the thermo-voltage distributions obtained using the most\ncommon method, the Non-equilibrium Green's function method, are qualitatively\ndifferent than those observed experimentally. We argue that this inconsistency\nbetween the theory and experiment is due to the level broadening, which is\ninherently built-in to the method, and smears out any variations of the\ntransmission on energy scales smaller than the level broadening. We show that\nalthough this smearing only weakly affects the transmission, it has a large\neffect on the calculated thermopower. Using the theory of open quantum systems\nwe account for both the magnitude of the variations and the qualitative form of\nthe distributions, and show that they arise not only from variations in the\nHOMO-Fermi level offset, but also from variations of the local density of\nstates at the contact point between the molecule and the electrode.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous Dynamical Behavior of Freestanding Graphene Membranes: We report subnanometer, high-bandwidth measurements of the out-of-plane\n(vertical) motion of atoms in freestanding graphene using scanning tunneling\nmicroscopy. By tracking the vertical position over a long time period, a\n1000-fold increase in the ability to measure space-time dynamics of atomically\nthin membranes is achieved over the current state-of-the-art imaging\ntechnologies. We observe that the vertical motion of a graphene membrane\nexhibits rare long-scale excursions characterized by both anomalous\nmean-squared displacements and Cauchy-Lorentz power law jump distributions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hamiltonian Description of Composite Fermions: Magnetoexciton\n  Dispersions: A microscopic Hamiltonian theory of the FQHE, developed by Shankar and myself\nbased on the fermionic Chern-Simons approach, has recently been quite\nsuccessful in calculating gaps in Fractional Quantum Hall states, and in\npredicting approximate scaling relations between the gaps of different\nfractions. I now apply this formalism towards computing magnetoexciton\ndispersions (including spin-flip dispersions) in the $\\nu=1/3$, 2/5, and 3/7\ngapped fractions, and find approximate agreement with numerical results. I also\nanalyse the evolution of these dispersions with increasing sample thickness,\nmodelled by a potential soft at high momenta. New results are obtained for\ninstabilities as a function of thickness for 2/5 and 3/7, and it is shown that\nthe spin-polarized 2/5 state, in contrast to the spin-polarized 1/3 state,\ncannot be described as a simple quantum ferromagnet.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hinge solitons in three-dimensional second-order topological insulators: A second-order topological insulator in three dimensions refers to a\ntopological insulator with gapless states localized on the hinges, which is a\ngeneralization of a traditional topological insulator with gapless states\nlocalized on the surfaces. Here we theoretically demonstrate the existence of\nstable solitons localized on the hinges of a second-order topological insulator\nin three dimensions when nonlinearity is involved. By means of systematic\nnumerical study, we find that the soliton has strong localization in real space\nand propagates along the hinge unidirectionally without changing its shape. We\nfurther construct an electric network to simulate the second-order topological\ninsulator. When a nonlinear inductor is appropriately involved, we find that\nthe system can support a bright soliton for the voltage distribution\ndemonstrated by stable time evolution of a voltage pulse.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Conduction Mechanism in a Molecular Hydrogen Contact: We present first principles calculations for the conductance of a hydrogen\nmolecule bridging a pair of Pt electrodes. The transmission function has a wide\nplateau with T~1 which extends across the Fermi level and indicates the\nexistence of a single, robust conductance channel with nearly perfect\ntransmission. Through a detailed Wannier function analysis we show that the H2\nbonding state is not involved in the transport and that the plateau forms due\nto strong hybridization between the H2 anti-bonding state and states on the\nadjacent Pt atoms. The Wannier functions furthermore allow us to derive a\nresonant-level model for the system with all parameters determined from the\nfully self-consistent Kohn-Sham Hamiltonian.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electronic structure of graphene-nanoribbons on hexagonal boron nitride: Hexagonal boron nitride is an ideal dielectric to form two-dimensional\nheterostructures due to the fact that it can be exfoliated to be just few atoms\nthick and its a very low density of defects. By placing graphene nanoribbons on\nhigh quality hexagonal boron nitride it is possible to create ideal quasi one\ndimensional (1D) systems with very high mobility. The availability of high\nquality one-dimensional electronic systems is of great interest also given that\nwhen in proximity to a superconductor they can be effectively engineered to\nrealize Majorana bound states. In this work we study how a boron nitride\nsubstrate affects the electronic properties of graphene nanoribbons. We\nconsider both armchair and zigzag nanoribbons. Our results show that for some\nstacking configurations the boron nitride can significantly affect the\nelectronic structure of the ribbons. In particular, for zigzag nanoribbons, due\nto the lock between spin and sublattice degree of freedom at the edges, the\nhexagonal boron nitride can induce a very strong spin-splitting of the spin\npolarized, edge sates. We find that such spin-splitting can be as high as\n40~meV.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Multiwalled Carbon Nanotubes as Building Blocks in Nanoelectronics: Molecular level components, like carbon multiwalled nanotubes (MWNT), show\ngreat potential for future nanoelectronics. At low frequencies, only the\noutermost carbon layer determines the transport properties of the MWNT. Due to\nthe multiwalled structure and large capacitive interlayer coupling, also the\ninner layers contribute to the conduction at high frequencies. Consequently,\nthe conduction properties of MWNTs are not very far from those of regular\nconductors with well-defined electrical characteristics. In our work we have\nexperimentally utilized this fact in constructing various nanoelectronic\ncomponents out of MWNTs, such as single electron transistors (SET), lumped\nresistors, and transmission lines. We present results on several nano- tube\nsamples, grown both using chemical vapor deposition as well as arc-discharge\nvaporization. Our results show that SET-electrometers with a noise level as low\nas 6x10^{-6}e/\\sqrt{Hz} (at 45 Hz) can be built using arc-discharge-grown\ncarbon nanotubes. Moreover, short nanotubes with small contact areas are found\nto work at 4.2 K with good gate modulation. Reactive ion etching on CVD tubes\nis employed to produce nearly Ohmic components with a resistance of 200 kOhm\nover a 2 micron section. At high frequencies, MWNTs work over micron distances\nas special LC-transmission lines with high impedance, on the order of 5 kOhm.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-Hermitian Chiral Magnetic Effect in Equilibrium: We analyze the Chiral Magnetic Effect for non-Hermitian fermionic systems\nusing the biorthogonal formulation of quantum mechanics. In contrast to the\nHermitian chiral counterparts, we show that the Chiral Magnetic Effect may take\nplace in thermal equilibrium of an open non-Hermitian system with, generally,\nmassive fermions. The key observation is that for non-Hermitian charged\nsystems, there is no strict charge conservation as understood in the Hermitian\ncase, so the Bloch theorem preventing currents in the thermodynamic limit in\nequilibrium does not apply.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Moir\u00e9 Flat Bands of Twisted Few-layer Graphite: We report that the twisted few layer graphite (tFL-graphite) is a new family\nof moir\\'{e} heterostructures (MHSs), which has richer and highly tunable\nmoir\\'{e} flat band structures entirely distinct from all the known MHSs. A\ntFL-graphite is composed of two few-layer graphite (Bernal stacked multilayer\ngraphene), which are stacked on each other with a small twisted angle. The\nmoir\\'{e} band structure of the tFL-graphite strongly depends on the layer\nnumber of its composed two van der Waals layers. Near the magic angle, a\ntFL-graphite always has two nearly flat bands coexisting with a few pairs of\nnarrowed dispersive (parabolic or linear) bands at the Fermi level, thus,\nenhances the DOS at $E_F$. This coexistence property may also enhance the\npossible superconductivity as been demonstrated in other multiband\nsuperconductivity systems. Therefore, we expect strong multiband correlation\neffects in tFL-graphite. Meanwhile, a proper perpendicular electric field can\ninduce several isolated nearly flat bands with nonzero valley Chern number in\nsome simple tFL-graphites, indicating that tFL-graphite is also a novel\ntopological flat band system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Robust Ferromagnetism in Silicene Nanoflakes through Patterned\n  Hydrogenation: Considerably different properties emerge in nanomaterials as a result of\nquantum confinement and edge effects. In this study, the electronic and\nmagnetic properties of quasi zero dimensional silicene nanoflakes (SiNFs) are\ninvestigated using first principles calculations. Whilst the zigzag edged\nhexagonal SiNFs exhibit nonmagnetic semiconducting character, the zigzag edged\ntriangular SiNFs are magnetic semiconductors. One effective method of\nharnessing the properties of silicene is hydrogenation owing to its\nreversibility and controllability. From bare SiNFs to half hydrogenated and\nthen to fully hydrogenated, a triangular SiNF experiences a change from\nferrimagnetic to very strong ferromagnetic, and then to non-magnetic.\nNonetheless, a hexagonal SiNF undergoes a transfer from nonmagnetic to very\nstrong ferromagnetic, then to nonmagnetic. The half hydrogenated SiNFs produce\na large spin moment that is directly proportional to the square of the flakes\nsize. It has been revealed that the strong induced spin magnetizations align\nparallel and demonstrates a collective character by large range ferromagnetic\nexchange coupling, giving rise to its potential use in spintronic circuit\ndevices. Spin switch models are offered as an example of one of the potential\napplications of SiNFs in tuning the transport properties by controlling the\nhydrogen coverage.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Impact of electrode density of states on transport through\n  pyridine-linked single molecule junctions: We study the impact of electrode band structure on transport through\nsingle-molecule junctions by measuring the conductance of pyridine-based\nmolecules using Ag and Au electrodes. Our experiments are carried out using the\nscanning tunneling microscope based break-junction technique and are supported\nby density functional theory based calculations. We find from both experiments\nand calculations that the coupling of the dominant transport orbital to the\nmetal is stronger for Au-based junctions when compared with Ag-based junctions.\nWe attribute this difference to relativistic effects, which results in an\nenhanced density of d-states at the Fermi energy for Au compared with Ag. We\nfurther show that the alignment of the conducting orbital relative to the Fermi\nlevel does not follow the work function difference between two metals and is\ndifferent for conjugated and saturated systems. We thus demonstrate that the\ndetails of the molecular level alignment and electronic coupling in\nmetal-organic interfaces do not follow simple rules, but are rather the\nconsequence of subtle local interactions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "SNS junctions in nanowires with spin-orbit coupling: role of confinement\n  and helicity on the sub-gap spectrum: We study normal transport and the sub-gap spectrum of\nsuperconductor-normal-superconductor (SNS) junctions made of semiconducting\nnanowires with strong Rashba spin-orbit coupling. We focus, in particular, on\nthe role of confinement effects in long ballistic junctions. In the normal\nregime, scattering at the two contacts gives rise to two distinct features in\nconductance, Fabry-Perot resonances and Fano dips. The latter arise in the\npresence of a strong Zeeman field $B$ that removes a spin sector in the leads\n(\\emph{helical} leads), but not in the central region. Conversely, a helical\ncentral region between non-helical leads exhibits helical gaps of half-quantum\nconductance, with superimposed helical Fabry-Perot oscillations. These normal\nfeatures translate into distinct subgap states when the leads become\nsuperconducting. In particular, Fabry-Perot resonances within the helical gap\nbecome parity-protected zero-energy states (parity crossings), well below the\ncritical field $B_c$ at which the superconducting leads become topological. As\na function of Zeeman field or Fermi energy, these zero-modes oscillate around\nzero energy, forming characteristic loops, which evolve continuously into\nMajorana bound states as $B$ exceeds $B_c$. The relation with the physics of\nparity crossings of Yu-Shiba-Rusinov bound states is discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The importance of chemical potential in the determination of water slip\n  in nanochannels: We investigate the slip properties of water confined in graphite-like\nnano-channels by non-equilibrium molecular dynamics simulations, with the aim\nof identifying and analyze separately the influence of different physical\nquantities on the slip length. In a system under confinement but connected to a\nreservoir of fluid, the chemical potential is the natural control parameter: we\nshow that two nanochannels characterized by the same macroscopic contact angle\n-- but a different microscopic surface potential -- do not exhibit the same\nslip length unless the chemical potential of water in the two channels is\nmatched. Some methodological issues related to the preparation of samples for\nthe comparative analysis in confined geometries are also discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Emergent Electromagnetic Induction and Adiabatic Charge Pumping in Weyl\n  Semimetals: The photovoltaic effect in a Weyl semimetal due to the adiabatic quantum\nphase is studied. We particularly focus on the case in which an external ac\nelectric field is applied to the semimetal. In this setup, we show that a\nphotocurrent is induced by the ac electric field. By considering a generalized\nWeyl Hamiltonian with nonlinear terms, it is shown that the photocurrent is\ninduced by circularly, rather than linearly, polarized light. This photovoltaic\ncurrent can be understood as an emergent electromagnetic induction in the\nmomentum space; the Weyl node is a magnetic monopole in the momentum space, of\nwhich the electric field is induced by the circular motion. This result is\ndistinct from conventional photovoltaic effects, and potentially useful for\nexperimentally identifying Weyl semimetals in chiral crystals.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Decoherence of Cooper pairs and subgap magnetoconductance of\n  superconducting hybrids: We demonstrate that electron-electron interactions fundamentally restrict the\npenetration length of superconducting correlations into a diffusive normal\nmetal (N) attached to a superconductor (S). We evaluate the subgap\nmagnetoconductance $G$ of SN hybrids in the presence of electron-electron\ninteractions and demonstrate that the effect of the magnetic field on $G$ is\ntwofold: It includes ($i$) additional temperature independent dephasing of\nCooper pairs and ($ii$) Zeeman splitting between the states with opposite\nspins. The dephasing length of Cooper pairs can be directly extracted from\nmeasurements of the subgap magnetoconductance in SN systems at low\ntemperatures.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermal transport controlled by intra- and inter-dot Coulomb\n  interactions in sequential and cotunneling serially-coupled double quantum\n  dots: We study thermoelectric transport through a serial double quantum dot (DQD)\ncoupled to two metallic leads with different thermal energies. We take into\naccount the electron sequential and cotunneling effects via different master\nequation approaches. In the absence of intra- and inter-dot Coulomb\ninteractions, a small peak in thermoelectric and heat currents is found for\n$E_{\\rm L} \\text{=} E_{\\rm R}$ indicating the Coulomb blockade DQD regime,\nwhere $E_{\\rm L}(E_{\\rm R})$ is the energy of the state of the left(right)\nquantum dot. In the presence of intra- and inter-dot Coulomb interactions with\nstrengths U$_{\\rm intra}$, and U$_{\\rm inter}$, respectively, avoided crossings\nor resonance energies between the intra- and the inter-dot two-electron states,\n2ES, are found. These resonances induce extra transport channels through the\nDQD leading to strong side peaks in the thermoelectric and heat currents at $\nE_{\\rm L} \\text{-} E_{\\rm R} = \\pm (U_{\\rm intra} \\text{-} U_{\\rm inter})$ in\naddition to the main peak generated at $E_{\\rm L} \\text{=} E_{\\rm R}$. The\ncurrent side peaks are enhanced by increased strength of the Coulomb\ninteractions. Interestingly, the current side peaks are enhanced when\ncotunneling terms are considered in which the resonances of the 2ESs assist the\nelectron cotunneling process through the system. Furthermore, the issue of\ncoherences is carefully checked in the DQD-leads system via different\napproaches to the master equation, which are the Pauli, the Redfield, a first\norder Lindblad, and the first- and second order von-Neumann methods. We realize\nthat the Pauli method gives a wrong results for the thermoelectric transport\nwhen the role of the coherences is relevant.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cooling of a Micro-mechanical Resonator by the Back-action of Lorentz\n  Force: Using a semi-classical approach, we describe an on-chip cooling protocol for\na micro-mechanical resonator by employing a superconducting flux qubit. A\nLorentz force, generated by the passive back-action of the resonator's\ndisplacement, can cool down the thermal motion of the mechanical resonator by\napplying an appropriate microwave drive to the qubit. We show that this onchip\ncooling protocol, with well-controlled cooling power and a tunable response\ntime of passive back-action, can be highly efficient. With feasible\nexperimental parameters, the effective mode temperature of a resonator could be\ncooled down by several orders of magnitude.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Charge-spin response and collective excitations in Weyl semimetals: Weyl semimetals are characterized by unconventional electromagnetic response.\nWe present analytical expressions for all components of the frequency- and\nwave-vector-dependent charge-spin linear-response tensor of Weyl fermions. The\nspin-momentum locking of the Weyl Hamiltonian leads to a coupling between\ncharge and longitudinal spin fluctuations, while transverse spin fluctuations\nremain decoupled from the charge. A real Weyl semimetal with multiple Weyl\nnodes can show this charge-spin coupling in equilibrium if its crystal symmetry\nis sufficiently low. All Weyl semimetals are expected to show this coupling if\nthey are driven into a non-equilibrium stationary state with different\noccupations of Weyl nodes, for example by exploiting the chiral anomaly. Based\non the response tensor, we investigate the low-energy collective excitations of\ninteracting Weyl fermions. For a local Hubbard interaction, the charge-spin\ncoupling leads to a dramatic change of the zero-sound dispersion: its velocity\nbecomes independent of the interaction strength and the chemical potential and\nis given solely by the Fermi velocity. In the presence of long-range Coulomb\ninteractions, the coupling transforms the plasmon modes into spin plasmons. For\nreal Weyl semimetals with multiple Weyl nodes, the collective modes are\nstrongly affected by the presence of parallel static electric and magnetic\nfields, due to the chiral anomaly. In particular, the zero-sound frequency at\nfixed momentum and the spin content of the spin plasmons go through cusp\nsingularities as the chemical potential of one of the Weyl cones is tuned\nthrough the Weyl node. We discuss possible experiments that could provide\nsmoking-gun evidence for Weyl physics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Heat dissipation and fluctuations in a driven quantum dot: While thermodynamics is a useful tool to describe the driving of large\nsystems close to equilibrium, fluctuations dominate the distribution of heat\nand work in small systems and far from equilibrium. We study the heat generated\nby driving a small system and change the drive parameters to analyse the\ntransition from a drive leaving the system close to equilibrium to driving it\nfar from equilibrium. Our system is a quantum dot in a GaAs/AlGaAs\nheterostructure hosting a two-dimensional electron gas. The dot is\ntunnel-coupled to one part of the two-dimensional electron gas acting as a heat\nand particle reservoir. We use standard rate equations to model the driven\ndot-reservoir system and find excellent agreement with the experiment.\nAdditionally, we quantify the fluctuations by experimentally test the\ntheoretical concept of the arrow of time, predicting our ability to distinguish\nwhether a process goes in the forward or backward drive direction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamic vibronic coupling in InGaAs quantum dots: The electron-phonon coupling in self-assembled InGaAs quantum dots is\nrelatively weak at low light intensities, which means that the zero-phonon line\nin emission is strong compared to the phonon sideband. However, the coupling to\nacoustic phonons can be dynamically enhanced in the presence of an intense\noptical pulse tuned within the phonon sideband. Recent experiments have shown\nthat this dynamic vibronic coupling can enable population inversion to be\nachieved when pumping with a blue-shifted laser and for rapid de-excitation of\nan inverted state with red detuning. In this paper we confirm the incoherent\nnature of the phonon-assisted pumping process and explore the temperature\ndependence of the mechanism. We also show that a combination of blue- and\nred-shifted pulses can create and destroy an exciton within a timescale ~20 ps\ndetermined by the pulse duration and ultimately limited by the phonon\nthermalisation time.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Landau Quantized Dynamics and Spectrum of the Diced Lattice: In this work the role of magnetic Landau quantization in the dynamics and\nspectrum of Diced Lattice charge carriers is studied in terms of the associated\npseudospin 1 Green's function. The equations of motion for the 9 matrix\nelements of this Green's function are formulated in position/frequency\nrepresentation and are solved explicitly in terms of a closed form integral\nrepresentation involving only elementary functions. The latter is subsequently\nexpanded in a Laguerre eigenfunction series whose frequency poles identify the\ndiscretized energy spectrum for the Landau-quantized Diced Lattice as\n$\\epsilon_n = \\pm\\sqrt{2(2n+1)\\alpha^2 eB}$ ($\\alpha\\sqrt{2}$ is the\ncharacteristic speed for the Diced Lattice) which differs significantly from\nthe nonrelativistic linear dependence of $\\epsilon_n$ on $B$, and is similar to\nthe corresponding $\\sqrt{B}-$dependence of other Dirac materials (Graphene,\nGroup VI Dichalcogenides).",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Carrier Injection and Scattering in Atomically Thin Chalcogenides: Atomically thin two-dimensional chalcogenides such as MoS2 monolayers are\nstructurally ideal channel materials for the ultimate atomic electronics.\nHowever, a heavy thickness dependence of electrical performance is shown in\nthese ultrathin materials, and the device performance normally degrades while\nexhibiting a low carrier mobility as compared with corresponding bulks,\nconstituting a main hurdle for application in electronics. In this brief\nreview, we summarize our recent work on electrode/channel contacts and carrier\nscattering mechanisms to address the origins of this adverse thickness\ndependence. Extrinsically, the Schottky barrier height increases at the\nelectrode/channel contact area in thin channels owing to bandgap expansion\ncaused by quantum confinement, which hinders carrier injection and degrades\ndevice performance. Intrinsically, thin channels tend to suffer from\nintensified Coulomb impurity scattering, resulting from the reduced interaction\ndistance between interfacial impurities and channel carriers. Both factors are\nresponsible for the adverse dependence of carrier mobility on channel thickness\nin two-dimensional semiconductors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Moir\u00e9 Imaging in Twisted Bilayer Graphene Aligned on Hexagonal Boron\n  Nitride: Moir\\'e superlattices (MSL) formed in angle-aligned bilayers of van der Waals\nmaterials have become a promising platform to realize novel two-dimensional\nelectronic states. Angle-aligned trilayer structures can form two sets of MSLs\nwhich could potentially interfere with each other. In this work, we directly\nimage the moir\\'e patterns in both monolayer graphene aligned on hBN and\ntwisted bilayer graphene aligned on hBN, using combined scanning microwave\nimpedance microscopy and conductive atomic force microscopy. Correlation of the\ntwo techniques reveals the contrast mechanism for the achieved ultrahigh\nspatial resolution (<2 nm). We observe two sets of MSLs with different\nperiodicities in the trilayer stack. The smaller MSL breaks the 6-fold\nrotational symmetry and exhibits abrupt discontinuities at the boundaries of\nthe larger MSL. Using a rigid atomic-stacking model, we demonstrate that the\nhBN layer considerably modifies the MSL of twisted bilayer graphene. We further\nanalyze its effect on the reciprocal space spectrum of the dual-moir\\'e system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Size dependent optical response in coupled systems of plasmons and\n  electron-hole pairs in metallic nanostructures: In bulk materials, the collective modes and individual modes are orthogonal\neach other, and no connection occurs if there is no damping processes. In the\npresence of damping, the collective modes, i.e., plasmons decay into the hot\ncarriers. In finite systems, the collective and individual modes are coupled by\nthe Coulomb interaction. Such couplings by longitudinal (L) field have been\nintensively investigated, whereas a coupling via transverse (T) field has been\npoorly studied although the plasmon is excited by an irradiated light on\nsurface and in finite nanostructures. Then, the T field would play a\nsignificant role in the coupling between the collective and individual\nexcitations. In this study, we investigate how the T field mediates the\ncoherent coupling. This study is based on the recently developed microscopic\nnonlocal theory of electronic systems in metals and the results of eigenmode\nanalyses by this theory. To tune the coupling strength in a single nanorod, we\nexamine three parameters: Rod length $L_z$, background refractive index $n_{\\rm\nb}$, and Fermi energy $\\varepsilon_{\\rm F}$. We discuss the modulation ratio of\nthe spectrum of optical response coefficients to evaluate the coupling by the T\nfield. The T field shifts the collective excitation energy, which causes a\nfinite modulation at both collective excitation and individual excitations. The\nthree parameters can change the energy distance between the collective and\nindividual excitations. Thus, the coherent coupling by the T field is enhanced\nfor a proper tuning of the parameters. The results of the investigation of\nsystem parameter dependence would give insight into the guiding principle of\ndesigning the materials for highly efficient hot carrier generation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Correlative nanoscale imaging of strained hBN spin defects: Spin defects like the negatively charged boron vacancy color center ($V_B^-$)\nin hexagonal boron nitride (hBN) may enable new forms of quantum sensing with\nnear-surface defects in layered van der Waals heterostructures. Here, we reveal\nthe effect of strain associated with creases in hBN flakes on $V_B^-$ and $V_B$\ncolor centers in hBN with correlative cathodoluminescence and photoluminescence\nmicroscopies. We observe strong localized enhancement and redshifting of the\n$V_B^-$ luminescence at creases, consistent with density functional theory\ncalculations showing $V_B^-$ migration toward regions with moderate uniaxial\ncompressive strain. The ability to manipulate these spin defects with highly\nlocalized strain offers intriguing possibilities for future 2D quantum sensors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical Charge Injection and Full Coherent Control of Spin-Qubit in the\n  Telecom C-band Emitting Quantum Dot: Solid-state quantum emitters with manipulable spin-qubits are promising\nplatforms for quantum communication applications. Although such light-matter\ninterfaces could be realized in many systems only a few allow for light\nemission in the telecom bands necessary for long-distance quantum networks.\nHere, we propose and implement a new optically active solid-state spin-qubit\nbased on a hole confined in a single InAs/GaAs quantum dot grown on an InGaAs\nmetamorphic buffer layer emitting photons in the C-band. We lift the hole\nspin-degeneracy using an external magnetic field and demonstrate hole\ninjection, initialization, read-out and complete coherent control using\npicosecond optical pulses. These results showcase a new solid-state spin-qubit\nplatform compatible with preexisting optical fibre networks.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Comparing two different descriptions of the I-V characteristic of\n  graphene: theory and experiment: The formalism of the nonperturbative description of transport phenomena in\ngraphene on the framework of the quantum kinetic equation for the\nSchwinger-like process is compared with the description on the basis of\nZener-Klein tunneling. The regime of ballistic conductivity in a constant\nelectric field is considered.\n  In the latter case the interaction of carriers with electric field is\ndescribed in terms of the spatial dependence of their potential energy\n(x-representation). The presented kinetic formalism uses an alternative method\nof describing the interaction with a field through the introduction of a\nquasimomentum $P=p-(e/c)A(t)$ where $A(t)$ is the vector potential\n(t-representation). Both approaches should lead to the same physical\ncharacteristics of the described process.\n  The measurement of the current in experiments is realized in static\nconditions determined by the potential difference between the electrodes and\nthe distance between them. These parameters are native for the\nx-representation. On the contrary, in the approach based on the\nt-representation it is necessary to consider the situation in dynamics and\nintroduce the effective lifetime of the generated carriers. In the ballistic\nregime this time depends on the distance between the electrodes.\n  We give a detailed comparison of these two descriptions of the current and\ndemonstrate good coincidence with the experimental data of the alternative\napproach based on the t-representation. It provides a reliable foundation for\nthe application of nonperturbative methods adopted from strong field QED, that\nallows to include in the consideration more general models of the field\n(arbitrary polarization and time dependence) and to extend the scope of the\ntheory.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological magnetic crystalline insulators and co-representation theory: Gapless surface states of time reversal invariant topological insulators are\nprotected by the anti-unitary nature of the time reversal operation. Very\nrecently, this idea was generalized to magnetic structures, in which time\nreversal symmetry is explicitly broken, but there is still an anti-unitary\nsymmetry operation combining time reversal symmetry and crystalline symmetry.\nThese topological phases in magnetic structures are dubbed \"topological\nmagnetic crystalline insulators\". In this work, we present a general theory of\ntopological magnetic crystalline insulators in different types of magnetic\ncrystals based on the co-representation theory of magnetic crystalline symmetry\ngroups. We construct two concrete tight-binding models of topological magnetic\ncrystalline insulators, the $\\hat{C}_4\\Theta$ model and the $\\hat{\\bf\n\\tau}\\Theta$ model, in which topological surface states and topological\ninvariants are calculated explicitly. Moreover, we check different types of\nanti-unitary operators in magnetic systems and find that the systems with\n$\\hat{C}_4\\Theta$, $\\hat{C}_6\\Theta$ and $\\hat{\\bf \\tau}\\Theta$ symmetry are\nable to protect gapless surface states. Our work will pave the way to search\nfor topological magnetic crystalline insulators in realistic magnetic\nmaterials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fano resonance in discrete lattice models: controlling lineshapes with\n  impurities: The possibility of controlling Fano lineshapes in the electronic transmission\nis addressed in terms of a simple discrete model within a tight binding\nframework, in which a finite sized ordered chain is coupled from one side to an\ninfinite linear chain (the `backbone') at one lattice point. It is found that,\nthe profile of Fano resonance is strongly influenced by the presence of\nimpurity atoms in the backbone. We specifically discuss the case with just two\nsubstitutional impurities sitting in the otherwise ordered backbone. Precise\nanalytical formulae relating the locations of these impurities to the size of\nthe side coupled chain have been presented. The nature of the transmission\nspectrum and the reversal of the pole-zero structures in the Fano resonance are\ndiscussed with the help of these formulae.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Band Symmetries and Singularities in Twisted Multilayer Graphene: The electronic spectra of rotationally faulted graphene bilayers are\ncalculated using a continuum formulation for small fault angles that identifies\ntwo distinct electronic states of the coupled system. The low energy spectra of\none state features a Fermi velocity reduction which ultimately leads to\npairwise annihilation and regeneration of its low energy Dirac nodes. The\nphysics in the complementary state is controlled by pseudospin selection rules\nthat prevent a Fermi velocity renormalization and produce second generation\nsymmetry-protected Dirac singularities in the spectrum. These results are\ncompared with previous theoretical analyses and with experimental data.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mechanical properties of carbynes investigated by ab initio total-energy\n  calculations: As sp carbon chains (carbynes) are relatively rigid molecular objects, can we\nexploit them as construction elements in nanomechanics? To answer this\nquestion, we investigate their remarkable mechanical properties by ab-initio\ntotal-energy simulations. In particular, we evaluate their linear response to\nsmall longitudinal and bending deformations and their failure limits for\nlongitudinal compression and elongation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-valley filtering in strained graphene structures with artificially\n  induced carrier mass and spin-orbit coupling: The interplay of massive electrons with spin-orbit coupling in bulk graphene\nresults in a spin-valley dependent gap. Thus, a barrier with such properties\ncan act as a filter, transmitting only opposite spins from opposite valleys. In\nthis Letter we show that strain induced pseudomagnetic field in such a barrier\nwill enforce opposite cyclotron trajectories for the filtered valleys, leading\nto their spatial separation. Since spin is coupled to the valley in the\nfiltered states, this also leads to spin separation, demonstrating a\nspin-valley filtering effect. The filtering behavior is found to be\ncontrollable by electrical gating as well as by strain.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mechanisms of radiation-induced degradation of hybryd perovskites based\n  solar cells and ways to increase their radiation tolerance: The basic processes of perovskite radiation resistance are discussed for\nphoto- and high-energy electron irradiation. It is shown that ionization of\niodine ions and a staged mechanism of elastic scattering (upon intermediate\nscattering on light ions of an organic molecule) lead to the formation of a\nrecombination center Ii. The features of ionization degradation of interfaces\nwith both planar and fractal structures are considered. A special type of\nfractality is identified, and its minimum possible level of photodegradation is\npredicted. By using the methodology of classical radiation physics, the Hoke\neffect was also studied, as well as the synergetics of cooperative phenomena in\ntandem systems. The principal channels for counteracting the radiation\ndegradation of solar cells based on hybrid perovskites have been revealed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Slowing down of spin relaxation in two dimensional systems by quantum\n  interference effects: The effect of weak localization on spin relaxation in a two-dimensional\nsystem with a spin-split spectrum is considered. It is shown that the spin\nrelaxation slows down due to the interference of electron waves moving along\nclosed paths in opposite directions. As a result, the averaged electron spin\ndecays at large times as $1/t$. It is found that the spin dynamics can be\ndescribed by a Boltzmann-type equation, in which the weak localization effects\nare taken into account as nonlocal-in-time corrections to the collision\nintegral. The corrections are expressed via a spin-dependent return\nprobability. The physical nature of the phenomenon is discussed and it is shown\nthat the \"nonbackscattering\" contribution to the weak localization plays an\nessential role. It is also demonstrated that the magnetic field, both\ntransversal and longitudinal, suppresses the power tail in the spin\npolarization.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-equilibrium spin-crossover in copper phthalocyanine: We demonstrate the tip induced control of the spin state of copper\nphthalocyanine (CuPc) on an insulator coated substrate. Accounting for\nelectronic correlations, we find that, under the condition of energetic\nproximity of neutral excited states to the anionic groundstate, the system can\nundergo a population inversion towards these excited states. The resulting\nstate of the system is accompanied by a change in the total spin quantum\nnumber. Experimental signatures of the crossover are the appearance of\nadditional nodal planes in the topographical STM images as well as a strong\nsuppression of the current near the center of the molecule. The robustness of\nthe effect against moderate charge conserving relaxation processes has also\nbeen tested.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Low field magnetotransport in strained Si/SiGe cavities: Low field magnetotransport revealing signatures of ballistic transport\neffects in strained Si/SiGe cavities is investigated. We fabricated strained\nSi/SiGe cavities by confining a high mobility Si/SiGe 2DEG in a bended nanowire\ngeometry defined by electron-beam lithography and reactive ion etching. The\nmain features observed in the low temperature magnetoresistance curves are the\npresence of a zero-field magnetoresistance peak and of an oscillatory structure\nat low fields. By adopting a simple geometrical model we explain the\noscillatory structure in terms of electron magnetic focusing. A detailed\nexamination of the zero-field peak lineshape clearly shows deviations from the\npredictions of ballistic weak localization theory.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Large insulating nitride islands on Cu3Au as a template for atomic spin\n  structures: We present controlled growth of c(2$\\times$2)N islands on the (100) surface\nof Cu$_3$Au, which can be used as an insulating surface template for\nmanipulation of magnetic adatoms. Compared to the commonly used\nCu(100)/c(2$\\times$2)N surface, where island sizes do not exceed several\nnanometers due to strain limitation, the current system provides better lattice\nmatching between metal and adsorption layer, allowing larger unstrained islands\nto be formed. We show that we can achieve island sizes ranging from tens to\nhundreds of nanometers, increasing the potential building area by a factor\n10$^3$. Initial manipulation attempts show no observable difference in adatom\nbehaviour, either in manipulation or spectroscopy.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalously large g-factor of single atoms adsorbed on a metal substrate: We have performed inelastic scanning tunneling spectroscopy (ISTS) on\nindividual Fe atoms adsorbed on a Ag(111) surface. ISTS reveals a magnetization\nexcitation with a lifetime of about 400 fsec which decreases linearly upon\napplication of a magnetic field. Astoundingly, we find that the g-factor, which\ncharacterizes the shift in energy of the excitation in a magnetic field, is g =\n3.1 instead of the regular value of 2. This enhancement can be understood when\nconsidering the complete electronic structure of both the Ag(111) surface state\nand the Fe atom, as shown by ab initio calculations of the magnetic\nsusceptibility.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electricity Harvested from Ambient Heat across Silicon Surface: We report that electricity can be generated from limitless thermal motion of\nions by two dimensional (2D) surface of silicon wafer at room temperature. A\ntypical silicon device, on which asymmetric electrodes with Au and Ag thin\nfilms were fabricated, can generate a typical open-circuit voltage up to 0.40 V\nin 5 M CuCl2 solution and an output current over 11 {\\mu}A when a 25 k{\\Omega}\nresistor was loaded into the circuit. Positive correlation between the output\ncurrent and the temperature, as well as the concentration, was observed. The\nmaximum output current and power density are 17 {\\mu}A and 8.6 {\\mu}W/cm2,\nrespectively. The possibility of chemical reaction was excluded by four groups\nof control experiments. A possible dynamic drag mechanism was proposed to\nexplain the experimental results. This finding further demonstrates that\nambient heat in the environment can be harvested by 2D semiconductor surfaces\nor low dimensional materials and would contribute significantly to the research\nof renewable energy. However, this finding does not agree with the second law\nof thermal dynamatics. A lot of future work will be needed to study the\nmechanism behind this phenomenon.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ge/Si nanowire mesoscopic Josephson junctions: The controlled growth of nanowires (NWs) with dimensions comparable to the\nFermi wavelengths of the charge carriers allows fundamental investigations of\nquantum confinement phenomena. Here, we present studies of proximity-induced\nsuperconductivity in undoped Ge/Si core/shell NW heterostructures contacted by\nsuperconducting leads. By using a top gate electrode to modulate the carrier\ndensity in the NW, the critical supercurrent can be tuned from zero to greater\nthan 100 nA. Furthermore, discrete sub-bands form in the NW due to confinement\nin the radial direction, which results in stepwise increases in the critical\ncurrent as a function of gate voltage. Transport measurements on these\nsuperconductor-NW-superconductor devices reveal high-order (n = 25) resonant\nmultiple Andreev reflections, indicating that the NW channel is smooth and the\ncharge transport is highly coherent. The ability to create and control coherent\nsuperconducting ordered states in semiconductor-superconductor hybrid\nnanostructures allows for new opportunities in the study of fundamental\nlow-dimensional superconductivity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Scalar-Interchange Potential and Magnetic/Thermodynamic Properties of\n  Graphene-like Materials: By means of numerical simulations, we explore possible effects of a special\ninterparticle interaction potential which is a function of external and\ninternal conditions of graphene-like systems. In addition to the\nelectromagnetic interaction, we introduce a new potential due to the exchange\nof a massive scalar, associated to the so-called Kekul\\'e deformations; this\ninteraction displays a spin-dependent profile. It turns out that the magnitude\nof Kekul\\'e deformation may significantly affect physical properties of\ngraphene. A Monte Carlo analysis enables one to analyze the behavior of the\nsystem under variation of the applied external field, temperature, and the\nparticular type of the exchanged excitation that induces the potential. We\npursue an investigation of the spin configurations, we analyze differences in\nthermal equilibrium magnetization and we carry out calculations of the magnetic\nsusceptibility and the specific heat in the presence of the Kekul\\'e-induced\nnew potential.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Induced magneto-conductivity in a two-node Weyl semimetal under Gaussian\n  random disorder: Measuring the magnetoconductivity induced from impurities may help determine\nthe impurity distribution and reveal the structure of a Weyl semimetal sample.\nTo verify this, we utilized the Gaussian random disorder to simulate charged\nimpurities in a two-node Weyl semimetal model and investigate the impact of\ncharged impurities on magnetoconductivity in Weyl semimetals. We first compute\nthe longitudinal magnetic conductivity and find that it is positive and\nincreases proportionally with the parameter governing the Gaussian distribution\nof charged impurities, suggesting the presence of negative longitudinal\nmagnetoresistivity (NLMR). Then we consider both the intravalley and\ninter-valley scattering processes to calculate the induced transverse\nmagnetoconductivity in the model. Our findings indicate that both inter-valley\nand intra-valley scattering processes play important roles in calculating the\ntransverse magnetoconductivity. The locations of Weyl nodes can also be\ndetermined by magnetoconductivity measurements. This is possible if the\nmagnetic field strength and the density of charged impurities are known.\nAlternatively, the measurement of magnetic conductivity may reveal the\ndistribution of charged impurites in a given sample once the locations of the\nWeyl nodes have been determined. These findings can aid in detecting the\nstructure of a Weyl semimetal sample, enhancing comprehension of\nmagnetotransport in Weyl semimetals, and promoting the development of valley\nelectronics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin Hall magnetoresistance in antiferromagnet/heavy-metal\n  heterostructures: We investigate the spin Hall magnetoresistance in thin film bilayer\nheterostructures of the heavy metal Pt and the antiferromagnetic insulator NiO.\nWhile rotating an external magnetic field in the easy plane of NiO, we record\nthe longitudinal and the transverse resistivity of the Pt layer and observe an\namplitude modulation consistent with the spin Hall magnetoresistance. In\ncomparison to Pt on collinear ferrimagnets, the modulation is phase shifted by\n90{\\deg} and its amplitude strongly increases with the magnitude of the\nmagnetic field. We explain the observed magnetic field-dependence of the spin\nHall magnetoresistance in a comprehensive model taking into account magnetic\nfield induced modifications of the domain structure in antiferromagnets. With\nthis generic model we are further able to estimate the strength of the\nmagnetoelastic coupling in antiferromagnets. Our detailed study shows that the\nspin Hall magnetoresistance is a versatile tool to investigate the magnetic\nspin structure as well as magnetoelastic effects, even in antiferromagnetic\nmultidomain materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Inverse design of reconfigurable piezoelectric topological phononic\n  plates: We present a methodology to perform inverse analysis on reconfigurable\ntopological insulators for flexural waves in plate-like structures. First the\nunit cell topology of a phononic plate is designed, which offers two-fold\ndegeneracy in the band structure by topology optimization. In the second step,\npiezoelectric patches bonded over the substrate plate are connected to an\nexternal circuit and used appropriately to break space inversion symmetry. The\nspace inversion symmetry breaking opens a topological band gap by mimicking\nquantum valley Hall effect. Numerical simulations demonstrate that the\ntopologically protected edge state exhibits wave propagation without\nbackscattering and is immune to disorders. Predominantly, the proposed idea\nenables real-time reconfigurability of the topological interfaces in waveguide\napplications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Temperature dependent electrical resistivity of a single strand of\n  ferromagnetic single crystalline nanowire: We have measured the electrical resistivity of a single strand of a\nferromagnetic Ni nanowire of diameter 55 nm using a 4-probe method in the\ntemperature range 3 K-300 K. The wire used is chemically pure and is a high\nquality oriented single crystalline sample in which the temperature independent\nresidual resistivity is determined predominantly by surface scattering. Precise\nevaluation of the temperature dependent resistivity ($\\rho$) allowed us to\nidentify quantitatively the electron-phonon contribution (characterized by a\nDebye temperature $\\theta_R$) as well as the spin-wave contribution which is\nsignificantly suppressed upon size reduction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Second- and third-order optical susceptibilities in bidimensional\n  semiconductors near excitons states: Semiconducting Transition Metal Dichalcogenides (TMDs) have significant\nnonlinear optical effects. In this work we have used second-harmonic generation\n(SHG) and the four-wave mixing (FWM) spectroscopy in resonance with the\nexcitons in MoS2, MoSe2, and WS2 monolayers to characterize the nonlinear\noptical properties of these materials. We show that trions and excitons are\nresponsible for enhancing the nonlinear optical response, and determine the\nexciton and trion energies by comparing with the photoluminescence spectra.\nMoreover, we extract the second and third order optical sheet susceptibility\nnear exciton energies and compare with values found in the literature. We also\ndemonstrate the ability to generate different nonlinear effects in a wide\nspectral range in the visible region for monolayer MoS2, opening the\npossibility of using two-dimensional materials for nonlinear optoelectronic and\nphotonic applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Unified theory of quantum phase transitions in quantum dots with gapped\n  host bands: We present a unified theory of quantum phase transitions for half-filled\nquantum dots (QDs) coupled to gapped host bands. We augment the bands by\nadditional weakly coupled metallic lead which allows us to analyze the system\nby using standard numerical renormalization group techniques. The ground state\nproperties of the systems without the additional metallic lead are then\nextrapolated in a controlled way from the broadened subgap spectral functions.\nWe show that a broad class of narrow-gap-semiconductor tunneling densities of\nstates (TDOSs) support the existence of two distinct phases known from their\nsuperconducting counterpart. Namely, $0$ phase which is marked by the singlet\nground state and the $\\pi$ phase regime with the doublet ground state. To keep\na close analogy with the superconducting case, we focus on the influence of\nparticle-hole asymmetry of the TDOS of the subgap spectral features.\nNevertheless, we also discus the possibility of inducing singlet-doublet\nquantum phase transitions in experimental setups by varying the filling of the\nQD. In addition, for gapped TDOS functions with smoothed gap edges, we\ndemonstrate that all subgap peaks may leak out of the gap into the continuous\npart of the spectrum, an effect which has no counterpart in the superconducting\nAnderson model.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Gate errors in solid state quantum computer architectures: We theoretically consider possible errors in solid state quantum computation\ndue to the interplay of the complex solid state environment and gate\nimperfections. In particular, we study two examples of gate operations in the\nopposite ends of the gate speed spectrum, an adiabatic gate operation in\nelectron-spin-based quantum dot quantum computation and a sudden gate operation\nin Cooper pair box superconducting quantum computation. We evaluate\nquantitatively the non-adiabatic operation of a two-qubit gate in a\ntwo-electron double quantum dot. We also analyze the non-sudden pulse gate in a\nCooper-pair-box-based quantum computer model. In both cases our numerical\nresults show strong influences of the higher excited states of the system on\nthe gate operation, clearly demonstrating the importance of a detailed\nunderstanding of the relevant Hilbert space structure on the quantum computer\noperations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Describing non-Hermitian dynamics using a Generalized Three-Time NEGF\n  for a Partition-free Molecular Junction with Electron-Phonon Coupling: In this paper we develop the Non-Equilibrium Green's Function (NEGF)\nformalism for a dissipative molecular junction that consists of a central\nmolecular system with one-dimensional electronic transport coupled to a phonon\nenvironment and attached to multiple electronic leads. Our approach is\npartitionless - initial preparation of the system places the whole system in\nthe correct canonical equilibrium state - and is valid for an external bias\nwith arbitrary time dependence. Using path integrals as an intermediary tool,\nwe apply a two-time Hubbard-Stratonovich transformation to the phonon influence\nfunctional with mixed real and imaginary times to obtain an exact expression\nfor the electronic density matrix at the expense of introducing coloured\nGaussian noises whose properties are rigorously derived from the environment\naction. This results in a unique stochastic Hamiltonian on each branch of the\nKonstantinov-Perel' contour (upper, lower, vertical) such that the time\nevolution operators in the Liouville equation no longer form a Hermitian\nconjugate pair, thus corresponding to non-Hermitian dynamics. To account for\nthis we develop a generalized three-time NEGF which is sensitive to all\nbranches of the contour, and relate it to the standard NEGF in the absence of\nphonons via a perturbative expansion of the noises. This approach is exact and\nfully general, describing the non-equilibrium driven dynamics from an initial\nthermal state while subject to inelastic scattering, and can be applied to\nnon-Hermitian dynamics in general.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Few-electron eigenstates of concentric double quantum rings: Few-electron eigenstates confined in coupled concentric double quantum rings\nare studied by the exact diagonalization technique. We show that the magnetic\nfield suppresses the tunnel coupling between the rings localizing the\nsingle-electron states in the internal ring, and the few-electron states in the\nexternal ring. The magnetic fields inducing the ground-state angular momentum\ntransitions are determined by the distribution of the electron charge between\nthe rings. The charge redistribution is translated into modifications of the\nfractional Aharonov-Bohm period. We demonstrate that the electron distribution\ncan be deduced from the cusp pattern of the chemical potentials governing the\nsingle-electron charging properties of the system. The evolution of the\nelectron-electron correlations to the high field limit of a classical Wigner\nmolecule is discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "One-Dimensional Quantum Confinement Effect Modulated Thermoelectric\n  Properties in InAs Nanowires: We report electrical conductance and thermopower measurements on InAs\nnanowires synthesized by chemical vapor deposition. Gate modulation of the\nthermopower of individual InAs nanowires with diameter around 20nm is obtained\nover T=40 to 300K. At low temperatures (T< ~100K), oscillations in the\nthermopower and power factor concomitant with the stepwise conductance\nincreases are observed as the gate voltage shifts the chemical potential of\nelectrons in InAs nanowire through quasi-one-dimensional (1D) sub-bands. This\nwork experimentally shows the possibility to modulate semiconductor nanowire's\nthermoelectric properties through the peaked 1D electronic density of states in\nthe diffusive transport regime, a long-sought goal in nanostructured\nthermoelectrics research. Moreover, we point out the importance of scattering\n(or disorder) induced energy level broadening in smearing out the 1D\nconfinement enhanced thermoelectric power factor at practical temperatures\n(e.g. 300K).",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Combining micro- and macroscopic probes to untangle single-ion and\n  spatial exchange anisotropies in a $S = 1$ quantum antiferromagnet: The magnetic ground state of the quasi-one-dimensional spin-1\nantiferromagnetic chain is sensitive to the relative sizes of the single-ion\nanisotropy ($D$) and the intrachain ($J$) and interchain ($J'$) exchange\ninteractions. The ratios $D/J$ and $J'/J$ dictate the material's placement in\none or other of three competing phases: a Haldane gapped phase, a quantum\nparamagnet and an XY-ordered state, with a quantum critical point at their\njunction. We have identified [Ni(HF)$_2$(pyz)$_2]$SbF$_6$, where pyz =\npyrazine, as a candidate in which this behavior can be explored in detail.\nCombining neutron scattering (elastic and inelastic) in applied magnetic fields\nof up to 10~tesla and magnetization measurements in fields of up to 60~tesla\nwith numerical modeling of experimental observables, we are able to obtain\naccurate values of all of the parameters of the Hamiltonian [$D = 13.3(1)$~K,\n$J = 10.4(3)$~K and $J' = 1.4(2)$~K], despite the polycrystalline nature of the\nsample. Density-functional theory calculations result in similar couplings ($J\n= 9.2$~K, $J' = 1.8$~K) and predict that the majority of the total spin\npopulation of resides on the Ni(II) ion, while the remaining spin density is\ndelocalized over both ligand types. The general procedures outlined in this\npaper permit phase boundaries and quantum-critical points to be explored in\nanisotropic systems for which single crystals are as yet unavailable.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Determination of universal critical exponents using Lee-Yang theory: Lee-Yang zeros are points in the complex plane of an external control\nparameter at which the partition function vanishes for a many-body system of\nfinite size. In the thermodynamic limit, the Lee-Yang zeros approach the\ncritical value on the real-axis, where a phase transition occurs. Partition\nfunction zeros have for many years been considered a purely theoretical\nconcept, however, the situation is changing now as Lee-Yang zeros have been\ndetermined in several recent experiments. Motivated by these developments, we\nhere devise a direct pathway from measurements of partition function zeros to\nthe determination of critical points and universal critical exponents of\ncontinuous phase transitions. To illustrate the feasibility of our approach, we\nextract the critical exponents of the Ising model in two and three dimensions\nfrom the fluctuations of the total energy and the magnetization in lattices of\nfinite size. Importantly, the critical exponents can be determined even if the\nsystem is away from the phase transition. Moreover, in contrast to standard\nmethods based on Binder cumulants, it is not necessary to drive the system\nacross the phase transition. As such, our method provides an intriguing\nperspective for investigations of phase transitions that may be hard to reach\nexperimentally, for instance at very low temperatures or at very high\npressures.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coherent transport in linear arrays of quantum dots: the effects of\n  period doubling and of quasi-periodicity: We evaluate the phase-coherent transport of electrons along linear structures\nof varying length, which are made from two types of potential wells set in\neither a periodic or a Fibonacci quasi-periodic sequence. The array is\ndescribed by a tight-binding Hamiltonian and is reduced to an effective dimer\nby means of a decimation-renormalization method, extended to allow for\nconnection to external metallic leads, and the transmission coefficient is\nevaluated in a T-matrix scattering approach. Parallel behaviors are found for\nthe energy dependence of the density of electron states and of the\ntransmittivity of the array. In particular, we explicitly show that on\nincreasing its length the periodic array undergoes a metal-insulator transition\nnear single occupancy per dot, whereas prominent pseudo-gaps emerge away from\nthe band center in the Fibonacci-ordered array.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Orbital gyrotropic magneto-electric effect and its strain engineering in\n  monolayer Nb$X_2$: Electrical control of the orbital degrees of freedom is an important area of\nresearch in the emerging field of \"orbitronics.\" Orbital {\\it gyrotropic}\nmagneto-electric effect (OGME) is the generation of an orbital magnetization in\na nonmagnetic metal by an applied electric field. Here, we show that strain\ninduces a large GME in the monolayer Nb$X_2$ ($X =$ S, Se) normal to the plane,\nprimarily driven by the orbital moments of the Bloch bands as opposed to the\nconventional spin magnetization, without any need for spin-orbit coupling. The\nkey physics is captured within an effective two-band valley-orbital model and\nit is shown to be driven by three key ingredients: the intrinsic valley orbital\nmoment, broken $C_{3z}$ symmetry, and strain-induced Fermi surface changes. The\neffect can be furthermore switched by changing the strain condition, with\npotential for future device applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coulomb-enhanced dynamic localization and Bell state generation in\n  coupled quantum dots: We investigate the dynamics of two interacting electrons in coupled quantum\ndots driven by an AC field. We find that the two electrons can be trapped in\none of the dots by the AC field, in spite of the strong Coulomb repulsion. In\nparticular, we find that the interaction may enhance the localization effect.\nWe also demonstrate the field excitation procedure to generate the maximally\nentangled Bell states. The generation time is determined by both analytic and\nnumerical solutions of the time dependent Schrodinger equation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Purcell effect at metal-insulator transitions: We investigate the spontaneous emission rate of a two-level quantum emitter\nnext to a composite medium made of randomly distributed metallic inclusions\nembedded in a dielectric host matrix. In the near-field, the Purcell factor can\nbe enhanced by two-orders of magnitude relative to the case of an homogeneous\nmetallic medium, and reaches its maximum precisely at the insulator-metal\ntransition. By unveiling the role of the decay pathways on the emitter's\nlifetime, we demonstrate that, close to the percolation threshold, the\nradiation emission process is dictated by electromagnetic absorption in the\nheterogeneous medium. We show that our findings are robust against change in\nmaterial properties, shape of inclusions, and apply for different effective\nmedium theories as well as for a wide range of transition frequencies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interlayer binding energy of graphite -- A direct experimental\n  determination: Despite interlayer binding energy is one of the most important material\nproperties for graphite, there is still lacking report on its direct\nexperimental determination. In this paper, we present a novel experimental\nmethod to directly measure the interlayer binding energy of highly oriented\npyrolytic graphite (HOPG). The obtained values of the binding energy are\n0.27($\\pm $0.02)J/m$^{2}$, which can serve as a benchmark for other theoretical\nand experimental works.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Observation of collapse of pseudospin order in bilayer quantum Hall\n  ferromagnets: The Hartree-Fock paradigm of bilayer quantum Hall states with finite\ntunneling at filling factor $\\nu$=1 has full pseudospin ferromagnetic order\nwith all the electrons in the lowest symmetric Landau level. Inelastic light\nscattering measurements of low energy spin excitations reveal major departures\nfrom the paradigm at relatively large tunneling gaps. The results indicate the\nemergence of a novel correlated quantum Hall state at $\\nu$=1 characterized by\nreduced pseudospin order. Marked anomalies occur in spin excitations when\npseudospin polarization collapses by application of in-plane magnetic fields.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Resonant plasmonic effects in periodic graphene antidot arrays: We show that a graphene sheet perforated with micro- or nano-size antidots\nhave prominent absorption resonances in the microwave and terahertz regions.\nThese resonances correspond to surface plasmons of a continuous sheet\n\"perturbed\" by a lattice. They are excited in different diffraction orders, in\ncontrast to cavity surface plasmon modes existing in disconnected graphene\nstructures. The resonant absorption by the antidot array can essentially exceed\nthe absorption by a continuous graphene sheet, even for high antidot\ndiameter-to-period aspect ratios. Surface plasmon-enhanced absorption and\nsuppressed transmission is more efficient for higher relaxation times of the\ncharge carriers.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Floquet approach to bichromatically driven cavity optomechanical systems: We develop a Floquet approach to solve time-periodic quantum Langevin\nequations in steady state. We show that two-time correlation functions of\nsystem operators can be expanded in a Fourier series and that a generalized\nWiener-Khinchin theorem relates the Fourier transform of their zeroth Fourier\ncomponent to the measured spectrum. We apply our framework to bichromatically\ndriven cavity optomechanical systems, a setting in which mechanical oscillators\nhave recently been prepared in quantum-squeezed states. Our method provides an\nintuitive way to calculate the power spectral densities for time-periodic\nquantum Langevin equations in arbitrary rotating frames.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A-geometrical approach to Topological Insulators with defects: The study of the propagation of electrons with a varying spinor orientability\nis performed using the coordinate transformation method. Topological Insulators\nare characterized by an odd number of changes of the orientability in the\nBrillouin zone. For defects the change in orientability takes place for closed\norbits in real space. Both cases are characterized by nontrivial spin\nconnections. Using this method , we derive the form of the spin connections for\ntopological defects in three dimensional Topological Insulators. On the surface\nof a Topological Insulator, the presence an edge dislocation gives rise to a\nspin connection controlled by torsion. We find that electrons propagate along\ntwo dimensional regions and confined circular contours. We compute for the edge\ndislocations the tunneling density of states. The edge dislocations violates\nparity symmetry resulting in a current measured by the in-plane component of\nthe spin on the surface.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamics of quantum cellular automata electron transition in triple\n  quantum dots: The quantum cellular automata (QCA) effect is a transition in which multiple\nelectron move coordinately by Coulomb interactions and observed in multiple\nquantum dots. This effect will be useful for realizing and improving quantum\ncellular automata and information transfer using multiple electron transfer. In\nthis paper, we investigate the real-time dynamics of the QCA charge transitions\nin a triple quantum dot by using fast charge-state readout realized by rf\nreflectometry. We observe real-time charge transitions and analyze the\ntunneling rate comparing with the first-order tunneling processes. We also\nmeasure the gate voltage dependence of the QCA transition and show that it can\nbe controlled by the voltage.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Microwave Rectification at the Boundary between Two-Dimensional Electron\n  Systems: Rectification of microwave radiation (20-40 GHz) by a line boundary between\ntwo two-dimensional metals on a silicon surface was observed and investigated\nat different temperatures, in-plane magnetic fields and microwave powers. The\nrectified voltage $V_{dc}$ is generated whenever the electron densities\n$n_{1,2}$ of the two metals are different, changing polarity at $n_1 \\approx\nn_2$. Very strong nonlinear response is found when one of the two 2D metals is\nclose to the electron density corresponding to the reported magnetic\ninstability in this system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum electrodynamic approach to the conductivity of gapped graphene: The electrical conductivity of graphene with a nonzero mass-gap parameter is\ninvestigated starting from the first principles of quantum electrodynamics in\n(2+1)-dimensional space-time at any temperature. The formalism of the\npolarization tensor defined over the entire plane of complex frequency is used.\nAt zero temperature we reproduce the results for both real and imaginary parts\nof the conductivity, obtained previously in the local approximation, and\ngeneralize them taking into account the effects of nonlocality. At nonzero\ntemperature the exact analytic expressions for real and imaginary parts of the\nlongitudinal and transverse conductivities of gapped graphene are derived, as\nwell as their local limits and approximate expressions in several asymptotic\nregimes. Specifically, a simple local result for the real part of conductivity\nof gapped graphene valid at any temperature is obtained. According to our\nresults, the real part of the conductivity is not equal to zero for frequencies\nexceeding the width of the gap and goes to the universal conductivity with\nincreasing frequency. The imaginary part of conductivity of gapped graphene\nvaries from infinity at zero frequency to minus infinity at the frequency\ndefined by the gap parameter and then goes to zero with further increase of\nfrequency. The analytic expressions are accompanied by the results of numerical\ncomputations. Possible future generalization of the used formalism is\ndiscussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-invasive detection of charge-rearrangement in a quantum dot in high\n  magnetic fields: We demonstrate electron redistribution caused by magnetic field on a single\nquantum dot measured by means of a quantum point contact as non-invasive\ndetector. Our device which is fabricated by local anodic oxidation allows to\ncontrol independently the quantum point contact and all tunnelling barriers of\nthe quantum dot. Thus we are able to measure both the change of the quantum dot\ncharge and also changes of the electron configuration at constant number of\nelectrons on the quantum dot. We use these features to exploit the quantum dot\nin a high magnetic field where transport through the quantum dot displays the\neffects of Landau shells and spin blockade. We confirm the internal\nrearrangement of electrons as function of the magnetic field for a fixed number\nof electrons on the quantum dot.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Monolithically integrated single quantum dots coupled to bowtie\n  nanoantennas: Deterministically integrating semiconductor quantum emitters with plasmonic\nnano-devices paves the way towards chip-scale integrable, true nanoscale\nquantum photonics technologies. For this purpose, stable and bright\nsemiconductor emitters are needed, which moreover allow for CMOS-compatibility\nand optical activity in the telecommunication band. Here, we demonstrate\nstrongly enhanced light-matter coupling of single near-surface ($<10\\,nm$) InAs\nquantum dots monolithically integrated into electromagnetic hot-spots of\nsub-wavelength sized metal nanoantennas. The antenna strongly enhances the\nemission intensity of single quantum dots by up to $\\sim16\\times$, an effect\naccompanied by an up to $3.4\\times$ Purcell-enhanced spontaneous emission rate.\nMoreover, the emission is strongly polarised along the antenna axis with\ndegrees of linear polarisation up to $\\sim85\\,\\%$. The results unambiguously\ndemonstrate the efficient coupling of individual quantum dots to\nstate-of-the-art nanoantennas. Our work provides new perspectives for the\nrealisation of quantum plasmonic sensors, step-changing photovoltaic devices,\nbright and ultrafast quantum light sources and efficent nano-lasers.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Emission and absorption asymmetry in the quantum noise of a Josephson\n  junction: We measure current fluctuations of mesoscopic devices in the quantum regime,\nwhen the frequency is of the order of or higher than the applied voltage or\ntemperature. Detection is designed to probe separately the absorption and\nemission contributions of current fluctuations, i.e. the positive and negative\nfrequencies of the Fourier transformed nonsymmetrized noise correlator. It\nrelies on measuring the quasiparticles photon assisted tunneling current across\na superconductor-insulator-superconductor junction (the detector junction)\ncaused by the excess current fluctuations generated by quasiparticles tunneling\nacross a Josephson junction (the source junction). We demonstrate unambiguously\nthat the negative and positive frequency parts of the nonsymmetrized noise\ncorrelator are separately detected and that the excess current fluctuations of\na voltage biased Josephson junction present a strong asymmetry between emission\nand absorption.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Bilayer WSe$_2$ as a natural platform for interlayer exciton condensates\n  in the strong coupling limit: Exciton condensates (EC) are macroscopic coherent states arising from\ncondensation of electron-hole pairs. Bilayer heterostructures, consisting of\ntwo-dimensional electron and hole layers separated by a tunnel barrier, provide\na versatile platform to realize and study EC. The tunnel barrier suppresses\nrecombination yielding long-lived excitons. However, this separation also\nreduces interlayer Coulomb interactions, limiting the exciton binding strength.\nHere, we report the observation of EC in naturally occurring 2H-stacked bilayer\nWSe$_2$. In this system, the intrinsic spin-valley structure suppresses\ninterlayer tunneling even when the separation is reduced to the atomic limit,\nproviding access to a previously unattainable regime of strong interlayer\ncoupling. Using capacitance spectroscopy, we investigate magneto-EC, formed\nwhen partially filled Landau levels (LL) couple between the layers. We find\nthat the strong-coupling EC show dramatically different behaviour compared with\nprevious reports, including an unanticipated variation of the EC robustness\nwith the orbital number, and find evidence for a transition between two types\nof low-energy charged excitations. Our results provide a demonstration of\ntuning EC properties by varying the constituent single-particle wavefunctions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cavity-enhanced measurements of defect spins in silicon carbide: The identification of new solid-state defect qubit candidates in widely used\nsemiconductors has the potential to enable the use of nanofabricated devices\nfor enhanced qubit measurement and control operations. In particular, the\nrecent discovery of optically active spin states in silicon carbide thin films\noffers a scalable route for incorporating defect qubits into on-chip photonic\ndevices. Here we demonstrate the use of 3C silicon carbide photonic crystal\ncavities for enhanced excitation of color center defect spin ensembles in order\nto increase measured photoluminescence signal count rates, optically detected\nmagnetic resonance signal intensities, and optical spin initialization rates.\nWe observe up to a factor of 30 increase in the photoluminescence and ODMR\nsignals from Ky5 color centers excited by cavity resonant excitation and\nincrease the rate of ground-state spin initialization by approximately a factor\nof two. Furthermore, we show that the small excitation mode volume and enhanced\nexcitation and collection efficiencies provided by the structures can be used\nto study inhomogeneous broadening in defect qubit ensembles. These results\nhighlight some of the benefits that nanofabricated devices offer for\nengineering the local photonic environment of color center defect qubits to\nenable applications in quantum information and sensing.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological Hall signatures of magnetic hopfions: Magnetic hopfions are topologically protected three-dimensional solitons that\nare constituted by a tube which exhibits a topologically nontrivial spin\ntexture in the cross-section profile and is closed to a torus. Here we show\nthat the hopfion's locally uncompensated emergent field leads to a topological\nHall signature, although the topological Hall effect vanishes on the global\nlevel. The topological Hall signature is switchable by magnetic fields or\nelectric currents and occurs independently of the anomalous and conventional\nHall effects. It can therefore be exploited to electrically detect hopfions in\nexperiments and even to distinguish them from other textures like skyrmion\ntubes. Furthermore, it can potentially be utilized in spintronic devices.\nExemplarily, we propose a hopfion-based racetrack data storage device and\nsimulate the electrical detection of the hopfions as carriers of information.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quasiparticle scattering off phase boundaries in epitaxial graphene: We investigate the electronic structure of terraces of single layer graphene\n(SLG) by scanning tunneling microscopy (STM) on samples grown by thermal\ndecomposition of 6H-SiC(0001) crystals in ultra-high vacuum. We focus on the\nperturbations of the local density of states (LDOS) in the vicinity of edges of\nSLG terraces. Armchair edges are found to favour intervalley quasiparticle\nscattering, leading to the (\\surd3\\times\\surd3)R30{\\deg} LDOS superstructure\nalready reported for graphite edges and more recently for SLG on SiC(0001).\nUsing Fourier transform of LDOS images, we demonstrate that the intrinsic\ndoping of SLG is responsible for a LDOS pattern at the Fermi energy which is\nmore complex than for neutral graphene or graphite, since it combines local\n(\\surd3\\times\\surd3)R30{\\deg} superstructure and long range beating modulation.\nAlthough these features were already reported by Yang et al. Nanoletters 10,\n943 (2010), we propose here an alternative interpretation based on simple\narguments classically used to describe standing wave patterns in standard\ntwo-dimensional systems. Finally, we discuss the absence of intervalley\nscattering off other typical boundaries: zig-zag edges and SLG/bilayer graphene\njunctions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "High-fidelity quantum memory utilizing inhomogeneous nuclear\n  polarization in a quantum dot: We numerically investigate the encoding and retrieval processes for a quantum\nmemory realized in a semiconductor quantum dot, by focusing on the effect of\ninhomogeneously polarized nuclear spins whose polarization depends on the local\nhyperfine coupling strength. We find that the performance of the quantum memory\nis significantly improved by the inhomogeneous nuclear polarization, as\ncompared to the homogeneous one. Moreover, the narrower the nuclear\npolarization distribution is, the better the performance of the quantum memory\nis. We ascribe the performance improvement to the full harnessing of the highly\npolarized and strongly coupled nuclear spins, by carefully studying the entropy\nchange of individual nuclear spins during encoding process. Our results shed\nnew light on the implementation of a quantum memory in a quantum dot.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Photon properties of single graphene nanoribbon microcavity laser: In this work, I propose a scheme about a single graphene nanoribbon (GNR)\nemitter in a microcavity, and focus on a fully-quantum-mechanical treatment\nmodel with the excitonic interaction included to investigate the photon\nproperties and lasing action. When the single armchair-edged GNRs (AGNRs)\nmicrocavity system is pumped, the exciton-photon coupling provides more photons\nand enhances the photon emission process, making it essentially a lasing\nobject. The theoretical results demonstrated that single AGNR in a\nsemiconductor microcavity system maybe serve as a nanolaser with ultralow\nlasing threshold.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spatial Confinement, Magnetic Localization and Their Interactions on\n  Massless Dirac Fermions: It is of keen interest to researchers understanding different approaches to\nconfine massless Dirac fermions in graphene, which is also a central problem in\nmaking electronic devices based on graphene. Here, we studied spatial\nconfinement, magnetic localization and their interactions on massless Dirac\nfermions in an angled graphene wedge formed by two linear graphene p-n\nboundaries with an angle 34. Using scanning tunneling microscopy, we visualized\nquasibound states temporarily confined in the studied graphene wedge. Large\nperpendicular magnetic fields condensed the massless Dirac fermions in the\ngraphene wedge into Landau levels (LLs). The spatial confinement of the wedge\naffects the Landau quantization, which enables us to experimentally measure the\nspatial extent of the wave functions of the LLs. The magnetic fields induce a\nsudden and large increase in energy of the quasibound states because of a pi\nBerry phase jump of the massless Dirac fermions in graphene. Such a behavior is\nthe hallmark of the Klein tunneling in graphene. Our experiment demonstrated\nthat the angled wedge is a unique system with the critical magnetic fields for\nthe pi Berry phase jump depending on distance from summit of the wedge.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Elastic strain field due to an inclusion of a polyhedral shape with a\n  non-uniform lattice misfit: An analytical solution in a closed form is obtained for the three-dimensional\nelastic strain distribution in an unlimited medium containing an inclusion with\na coordinate-dependent lattice mismatch (an eigenstrain). Quantum dots\nconsisting of a solid solution with a spatially varying composition are\nexamples of such inclusions. It is assumed that both the inclusion and the\nsurrounding medium (the matrix) are elastically isotropic and have the same\nYoung modulus and Poisson ratio. The inclusion shape is supposed to be an\narbitrary polyhedron, and the coordinate dependence of the lattice misfit, with\nrespect to the matrix, is assumed to be a polynomial of any degree. It is shown\nthat, both inside and outside the inclusion, the strain tensor is expressed as\na sum of contributions of all faces, edges and vertices of the inclusion. Each\nof these contributions, as a function of the observation point's coordinates,\nis a product of some polynomial and a simple analytical function, which is the\nsolid angle subtended by the face from the observation point (for a\ncontribution of a face), or the potential of the uniformly charged edge (for a\ncontribution of an edge), or the distance from the vertex to the observation\npoint (for a contribution of a vertex). The method of constructing the relevant\npolynomial functions is suggested. We also found out that similar expressions\ndescribe an electrostatic or gravitational potential, as well as its first and\nsecond derivatives, of a polyhedral body with a charge/mass density that\ndepends on coordinates polynomially.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hot exciton relaxation in coupled ultra-thin CdTe/ZnTe quantum well\n  structures: The photoluminescence (PL) and PL excitation (PLE) spectra of CdTe/ZnTe\nasymmetric double quantum well (QW) structures are studied on a series of\nsamples containing two CdTe layers with nominal thicknesses of 2 and 4\nmonolayers (ML) in the ZnTe matrix. The samples differ in the thickness of the\nZnTe spacer between CdTe QWs which is 45, 65 and 75 ML. It has been found that\nat above-barrier excitation the PL from a shallow QW at sufficiently weak\nexcitation intensities is determined by recombination of hot excitons. It is\nshown that under these conditions, when PL is excited by lasers with different\nwavelengths, the ratio of the PL intensities from shallow and deep QWs\ndecreases exponentially with an increase of the initial kinetic energy of hot\nexcitons. It is found that energy relaxation of hot excitons with LO phonon\nemission determine the shape of the PLE spectrum of shallow QW in the range of\nexciton kinetic energies up to more than 20 LO phonons above ZnTe bandgap. We\nhave shown that the results obtained are well described by the model of charge\nand energy transfer between QWs.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Influence of Nuclear Quadrupole Moments on Electron Spin Coherence in\n  Semiconductor Quantum Dots: We theoretically investigate the influence of the fluctuating Overhauser\nfield on the spin of an electron confined to a quantum dot (QD). The\nfluctuations arise from nuclear angular momentum being exchanged between\ndifferent nuclei via the nuclear magnetic dipole coupling. We focus on the role\nof the nuclear electric quadrupole moments (QPMs), which generally cause a\nreduction in internuclear spin transfer efficiency in the presence of electric\nfield gradients. The effects on the electron spin coherence time are studied by\nmodeling an electron spin echo experiment. We find that the QPMs cause an\nincrease in the electron spin coherence time and that an inhomogeneous\ndistribution of the quadrupolar shift, where different nuclei have different\nshifts in energy, causes an even larger increase in the electron coherence time\nthan a homogeneous distribution. Furthermore, a partial polarization of the\nnuclear spin ensemble amplifies the effect of the inhomogeneous quadrupolar\nshifts, causing an additional increase in electron coherence time, and provides\nan alternative to the experimentally challenging suggestion of full dynamic\nnuclear spin polarization.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ultrafast Relaxation Dynamics of Photoexcited Dirac Fermion in The Three\n  Dimensional Dirac Semimetal Cadmium Arsenide: Three dimensional (3D) Dirac semimetals which can be seen as 3D analogues of\ngraphene have attracted enormous interests in research recently. In order to\napply these ultrahigh-mobility materials in future electronic/optoelectronic\ndevices, it is crucial to understand the relaxation dynamics of photoexcited\ncarriers and their coupling with lattice. In this work, we report ultrafast\ntransient reflection measurements of the photoexcited carrier dynamics in\ncadmium arsenide (Cd3As2), which is one of the most stable Dirac semimetals\nthat have been confirmed experimentally. By using low energy probe photon of\n0.3 eV, we probed the dynamics of the photoexcited carriers that are\nDirac-Fermi-like approaching the Dirac point. We systematically studied the\ntransient reflection on bulk and nanoplate samples that have different doping\nintensities by tuning the probe wavelength, pump power and lattice temperature,\nand find that the dynamical evolution of carrier distributions can be retrieved\nqualitatively by using a two-temperature model. This result is very similar to\nthat of graphene, but the carrier cooling through the optical phonon couplings\nis slower and lasts over larger electron temperature range because the optical\nphonon energies in Cd3As2 are much lower than those in graphene.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Carbon Nanotube Thermal Transport: Ballistic to Diffusive: We propose to use l_0/(l_0+L) for the energy transmission covering both\nballistic and diffusive regimes, where l_0 is mean free path and L is system\nlength. This formula is applied to heat conduction in carbon nanotubes (CNTs).\nCalculations of thermal conduction show: (1) Thermal conductance at room\ntemperature is proportional to the diameter of CNTs for single-walled CNTs\n(SWCNTs) and to the square of diameter for multi-walled CNTs (MWCNTs). (2)\nInterfaces play an important role in thermal conduction in CNTs due to the\nsymmetry of CNTs vibrational modes. (3) When the phonon mean free path is\ncomparable with the length L of CNTs in ballistic-diffusive regime, thermal\nconductivity \\kappa goes as L^{\\alpha} . The effective exponent \\alpha is\nnumerically found to decrease with increasing temperature and is insensitive to\nthe diameter of SWCNTs for Umklapp scattering process. For short SWCNTs (<0.1\n\\mu m) we find \\alpha \\approx 0.8 at room temperature. These results are\nconsistent with recent experimental findings.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Practical Guide to Quantum Phase Transitions in Quantum-Dot-Based\n  Tunable Josephson Junctions: Quantum dots attached to BCS superconducting leads exhibit a $0-\\pi$ impurity\nquantum phase transition, which can be experimentally controlled either by the\ngate voltage or by the superconducting phase difference. For the pertinent\nsuperconducting single-impurity Anderson model, we newly present two simple\nanalytical formulae describing the position of the phase boundary in parameter\nspace for the weakly correlated and Kondo regime, respectively. Furthermore, we\nshow that the two-level approximation provides an excellent description of the\nlow temperature physics of superconducting quantum dots near the phase\ntransition. We discuss reliability and mutual agreement of available finite\ntemperature numerical methods (Numerical Renormalization Group and Quantum\nMonte Carlo) and suggest a novel approach for efficient determination of the\nquantum phase boundary from measured finite temperature data. Our results\nenable fast and efficient, yet reliable characterization and design of such\nnanoscopic tunable Josephson junction devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Giant Magneto-Oscillations of Electric-Field-Induced Spin Polarization\n  in 2DEG: We consider a disordered two-dimensional electron gas with spin-orbit\ncoupling placed in a perpendicular magnetic field and calculate the magnitude\nand direction of the electric-field-induced spin polarization. We find that in\nstrong magnetic fields the polarization becomes an oscillatory function of the\nmagnetic field and that the amplitude of these oscillations is parametrically\nlarger than the polarization at zero magnetic field. We show that the enhanced\namplitude of the polarization is a consequence of strong electron-hole\nasymmetry in a quantizing magnetic field.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic Response in Mesoscopic Rings and Moebius Strips: A Theoretical\n  Study: We investigate magnetic response in mesoscopic rings and moebius strips\npenetrated by magnetic flux $\\phi$. Based on a simple tight-binding framework\nall the calculations are performed numerically which describe persistent\ncurrent and low-field magnetic susceptibility as functions of magnetic flux\n$\\phi$, total number of electrons $N_e$, system size $N$ and disorder strength\n$W$. Our exact analysis may provide some important signatures to study magnetic\nresponse in nano-scale loop geometries.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Shot noise in diffusive conductors: A quantitative analysis of\n  electron-phonon interaction effects: Using the 'drift-diffusion-Langevin' equation, we have quantitatively\nanalyzed the effects of electron energy relaxation via their interaction with\nphonons, generally in presence of electron-electron interaction, on shot noise\nin diffusive conductors. We have found that the noise power $ S_I(\\omega )$\n(both at low and high observation frequencies $\\omega $) drops to half of its\n'mesoscopic' value only at $\\beta \\gtrsim 100,$ where $\\beta $ is the ratio of\nthe sample length $L$ to the energy relaxation length $l_{% {\\rm ph}}$ (the\nlatter may be much larger then the dephasing length). It means in particular\nthat at low temperatures the shot noise may be substantial even when $L\\sim\n10^{-2}$ -- $10^{-1}$ cm, and the conductor is 'macroscopic' in any other\nrespect.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic translations for a spatially periodic magnetic field: It is shown that in the case of free electron in a spatially periodic\nmagnetic field the concept of magnetic translations operators is still valid\nand, moreover, these operators can be defined in the same way as for a Bloch\nelectron in a uniform magnetic field. The results can be a useful tool in\ninvestigation of lately observed phenomena in 2DEG with spatially modulated\ndensity.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "PT Symmetric Floquet Topological Phase: In this paper, we study the existence of Floquet topological insulators for\nPT symmetric non-Hermitian Hamiltonians. We consider an array of waveguide in\n1D with periodically changing non-Hermitian potential and predict the existence\nof Floquet topological insulators in the system. We also extend the concept of\nFloquet topological phase to a two dimensional non-Hermitian system.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Enhanced longevity of the spin helix in low-symmetry quantum wells: In a semiconductor, collective excitations of spin textures usually decay\nrather fast due to D'yakonov-Perel' spin relaxation. The latter arises from\nspin-orbit coupling, which induces wave-vector-dependent spin rotations that,\nin conjunction with random disorder scattering, generate spin decoherence.\nHowever, symmetries occurring under certain conditions can prevent the\nrelaxation of particular homogeneous and inhomogeneous spin textures. The\ninhomogeneous spin texture, termed as persistent spin helix, is especially\nappealing as it enables us to manipulate the spin orientation while retaining a\nlong spin lifetime. Recently, it was predicted that such symmetries can be\nrealized in zinc-blende two-dimensional electron gases if at least two\ngrowth-direction Miller indices agree in modulus and the coefficients of the\nRashba and linear Dresselhaus spin-orbit couplings are suitably matched [PRL\n117, 236801 (2016)]. In the present paper, we systematically analyze the impact\nof the symmetry-breaking cubic Dresselhaus spin-orbit coupling, which\ngenerically coexists in these systems, on the stability of the emerging spin\nhelices with respect to the growth direction. We find that, as an interplay\nbetween orientation and strength of the effective magnetic field induced by the\ncubic Dresselhaus terms, the spin relaxation is weakest for a low-symmetry\ngrowth direction that can be well approximated by a [225] lattice vector. These\nquantum wells yield a 30\\% spin-helix lifetime enhancement compared to\n[001]-oriented electron gases and, remarkably, require a negligible Rashba\ncoefficient. The rotation axis of the corresponding spin helix is only slightly\ntilted out of the quantum-well plane. This makes the experimental study of the\nspin-helix dynamics readily accessible for conventional optical spin\norientation measurements where spins are excited and detected along the\nquantum-well growth direction.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optimized Tersoff and Brenner empirical potential parameters for lattice\n  dynamics and phonon thermal transport in carbon nanotubes and graphene: We have examined the commonly used Tersoff and Brenner empirical interatomic\npotentials in the context of the phonon dispersions in graphene. We have found\na parameter set for each empirical potential that provides improved fits to\nsome structural data and to the in-plane phonon dispersion data for graphite.\nThese optimized parameter sets yield values of the acoustic phonon velocities\nthat are in better agreement with measured data. They also provide lattice\nthermal conductivity values in single-walled carbon nanotubes that are\nconsiderably improved compared to those obtained from the original parameter\nsets.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetic Splitting of the Zero Bias Peak in a Quantum Point Contact with\n  a Variable Aspect Ratio: We report a zero-bias peak in the differential conductance of a Quantum Point\nContact (QPC), which splits in an external magnetic field. The peak is observed\nover a range of device conductance values starting significantly below\n$2e^2/h$. The observed splitting closely matches the Zeeman energy and shows\nvery little dependence on gate voltage, suggesting that the mechanism\nresponsible for the formation of the peak involves electron spin. Precision\nZeeman energy data for the experiment are obtained from a separately patterned\nsingle-electron transistor located a short distance away from the QPC. The QPC\ndevice has four gates arranged in a way that permits tuning of the longitudinal\npotential, and is fabricated in a GaAs/AlGaAs heterostructure containing\n2-dimenional electron gas. We show that the agreement between the peak\nsplitting and the Zeeman energy is robust with respect to moderate distortions\nof the QPC potential. We also show that the mechanism that leads to the\nformation of the ZBP is different from the conventional Kondo effect found in\nquantum dots.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport Study of Charge Carrier Scattering in Monolayer WSe$_2$: Employing flux-grown single crystal WSe$_2$, we report charge carrier\nscattering behaviors measured in $h$-BN encapsulated monolayer field effect\ntransistors. We perform quantum transport measurements across various hole\ndensities and temperatures and observe a non-monotonic change of transport\nmobility $\\mu$ as a function of hole density in the degenerately doped sample.\nThis unusual behavior can be explained by energy dependent scattering amplitude\nof strong defects calculated using the T-matrix approximation. Utilizing long\nmean-free path ($>$500 nm), we demonstrate the high quality of our electronic\ndevices by showing quantized conductance steps from an\nelectrostatically-defined quantum point contact. Our results show the potential\nfor creating ultra-high quality quantum optoelectronic devices based on\natomically thin semiconductors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetically induced oscillations of the spin polarization in the\n  Datta-Das geometry: The control of intrinsic magnetic degrees of freedom is very important as it\noffers a practical means to manipulate and probe electron spin transport.\nTunable spin-orbit effect in quantum wires can in principle serve as a means to\nachieve this goal. Here, we investigate within the scattering matrix approach\nthe effect of an in-plane magnetic field on the conductance of the quantum wire\nin the Datta-Das geometry and show that the interplay of the spin-orbit\ninteraction with the magnetic field provides enhanced control over the electron\nspin polarization. In particular, we predict a novel effect of magnetically\ninduced oscillations of the electron spin in a certain range of magnetic field.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Vacancy-induced localized modes and impurity band formation in the\n  Haldane model: a quantum dot analogy: In this study, the Haldane model's edge states are utilized to illustrate\nthat a zero-energy localized state forms around a single vacancy in the model.\nIn order to complete this task, the conventional unit cell associated to the\nHaldane hexagonal structure is transferred onto a two-leg ladder in momentum\nspace, effectively forming an extended Su-Schrieffer-Heeger~(SSH) lattice\nthrough a one-dimensional Fourier transform. Through the application of a\nsuitable unitary transformation, the two-leg SSH ladder in momentum space is\nconverted into an equivalent lattice with two distinct on-site states with\ndifferent momentum that are suitable for the calculations. Ultimately, the\ndesired zero-energy localized mode formed around the vacant-site is represented\nby a combination of the armchair edge states. Furthermore, the scenario\ninvolving two vacant sites is investigated and it is revealed that an effective\nhopping interaction exists between the localized states formed around the\non-site vacancies created along a zigzag chain in the lattice. This structure\ncan be likened to the structure of a quantum dot with two none-degenerate\nenergy levels. Such a hopping interaction is absent for the same vacancies\ncreated on the armchair chains. Finally, it is shown that introducing vacancies\nperiodically on the sites of a zigzag row along a finite-width ribbon with the\nHaldane structure leads to the emergence of an impurity band within the energy\ngap.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cryogenic spin Seebeck effect: We present a theory of the non-linearities of the spin Seebeck effect (SSE)\nin a ferromagnetic nanowire at cryogenic temperatures. We adopt a microscopic\nquantum noise model based on a collection of two-level systems. At certain\npositions of Pt detectors to the wire, the transverse SSE changes sign as a\nfunction of temperature and/or temperature gradient. On the other hand, the\nlongitudinal SSE does not show significant non-linearities even far outside the\nregime of validity of linear response theory.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunable ferroelectricity in hBN intercalated twisted double-layer\n  graphene: Van der Waals (vdW) assembly of two-dimensional materials has been long\nrecognized as a powerful tool to create unique systems with properties that\ncannot be found in natural compounds. However, among the variety of vdW\nheterostructures and their various properties, only a few have revealed\nmetallic and ferroelectric behaviour signatures. Here we show ferroelectric\nsemimetal made of double-gated double-layer graphene separated by an atomically\nthin crystal of hexagonal boron nitride, which demonstrating high room\ntemperature mobility of the order of 10 m$^2$V$^{-1}$s$^{-1}$ and exhibits\nrobust ambipolar switching in response to the external electric field. The\nobserved hysteresis is tunable, reversible and persists above room temperature.\nOur fabrication method expands the family of ferroelectric vdW compounds and\noffers a route for developing novel phase-changing devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "On the Implications of Discrete Symmetries for the Beta Function of\n  Quantum Hall Systems: We argue that the large discrete symmetry group of quantum Hall systems is\ninsufficient in itself to determine the complete beta function for the scaling\nof the conductivities, $\\sigma_{xx}$ and $\\sigma_{xy}$. We illustrate this\npoint by showing that a recent ansatz for this function is one of a\nmany-parameter family. A clean prediction for the delocalization exponents for\nthese systems therefore requires the specification of more information, such as\npast proposals that the beta function is either holomorphic or\nquasi-holomorphic in the variable $z = (\\hbar/e^2)(\\sigma_{xy} +\ni\\sigma_{xx})$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Large quantum nonlinear dynamic susceptibility of single-molecule\n  magnets: The nonlinear dynamical response of Mn$_{12}$ single-molecule magnets is\nexperimentally found to be very large, quite insensitive to the spin-lattice\ncoupling constant, and displaying peaks reversed with respect to classical\nsuperparamagnets. It is shown that these features are caused by the strong\nfield dependence of the relaxation rate due to the detuning of energy levels\nbetween which tunneling takes place. The nonlinear susceptibility technique,\npreviously overlooked, is thus proposed as a privileged probe to ascertain the\noccurrence of quantum effects in mesoscopic magnetic systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The electronic properties of doped single walled carbon nanotubes and\n  carbon nanotube sensors: We present ab initio calculations on the band structure and density of states\nof single wall semiconducting carbon nanotubes with high degrees (up to 25%) of\nB, Si and N substitution. The doping process consists of two phases: different\ncarbon nanotubes (CNTs) for a constant doping rate and different doping rates\nfor the zigzag (8, 0) carbon nanotube. We analyze the doping dependence of\nnanotubes on the doping rate and the nanotube type. Using these results, we\nselect the zigzag (8, 0) carbon nanotube for toxic gas sensor calculation and\nobtain the total and partial densities of states for CNT (8, 0). We have\ndemonstrated that the CNT (8, 0) can be used as toxic gas sensors for CO and NO\nmolecules, and it can partially detect Cl$_2$ toxic molecules but cannot detect\nH$_2$S. To overcome these restrictions, we created the B and N doped CNT (8, 0)\nand obtained the total and partial density of states for these structures. We\nalso showed that B and N doped CNT (8, 0) can be used as toxic gas sensors for\nsuch molecules as CO, NO, Cl$_2$ and H$_2$S.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Trigonal distortion of topologically confined channels in bilayer\n  Graphene: In this work we show that the trigonal warping of the electronic bands in\nbilayer graphene dramatically modifies the behavior of the one-dimensional\nmodes topologically confined due to an inhomogeneous bias that changes sign\nacross a channel. The topologically protected states are present but their\nbehavior is disrupted from the predicted in the isotropic approximation. We\npresent detailed studies of the electronic properties of the 1D channel in\nfunction of the orientation of the channel.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Oligothiophene nano-rings as electron resonators for whispering gallery\n  modes: Structural and electronic properties of oligothiophene nano-wires and rings\nsynthesized on a Au(111) surface are investigated by scanning tunneling\nmicroscopy. The spectroscopic data of the linear and cyclic oligomers show\nremarkable differences which, to a first approximation, can be accounted by\nconsidering electronic states confinement to one-dimensional (1D) boxes having\nrespectively fixed and periodic boundary conditions. A more detailed analysis\nshows that polythiophene must be treated as a ribbon (i.e. having an effective\nwidth) rather than a purely 1D structure. A fascinating consequence is that the\nmolecular nano-rings act as whispering gallery mode resonators for electrons,\nopening the way for new applications in quantum-electronics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamical separation of bulk and edge transport in HgTe-based 2D\n  topological insulators: Topological effects in edge states are clearly visible on short lengths only,\nthus largely impeding their studies. On larger distances, one may be able to\ndynamically enhance topological signatures by exploiting the high mobility of\nedge states with respect to bulk carriers. Our work on microwave spectroscopy\nhighlights the responses of the edges which host very mobile carriers, while\nbulk carriers are drastically slowed down in the gap. Though the edges are\ndenser than expected, we establish that charge relaxation occurs on short\ntimescales, and suggests that edge states can be addressed selectively on\ntimescales over which bulk carriers are frozen.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magneto-elastic universal logic gate: A non-volatile, error-resilient\n  Boolean logic gate with ultra-low energy-delay product: A long-standing goal of computer technology is to process and store digital\ninformation with the same device in order to implement new architectures. One\nway to accomplish this is to use nanomagnetic `non-volatile' logic gates that\ncan perform Boolean operations and then store the output data in the\nmagnetization states of nanomagnets, thereby doubling as both logic and memory.\nUnfortunately, many proposed nanomagnetic gates do not possess the seven\nessential characteristics of a Boolean logic gate: concatenability,\nnon-linearity, isolation between input and output, gain, universal logic\nimplementation, scalability and error resilience. More importantly, their\nenergy-delay products and error-rates vastly exceed that of conventional\ntransistor-based logic gates, which is a drawback. Here, we propose a\nnon-volatile voltage-controlled nanomagnetic logic gate that possesses all the\nnecessary characteristics of a logic gate and whose energy-delay product is ~2\norders of magnitude less than that of other nano-magnetic (non-volatile) logic\ngates and ~1 order of magnitude less than that of (volatile) CMOS-based logic\ngates. The error-resilience is also superior to that of other known\nnanomagnetic gates.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Superfluidity of Dipolar Excitons in a Black Phosphorene Double Layer: We study the formation of dipolar excitons and their superfluidity in a black\nphosphorene double layer. The analytical expressions for the single dipolar\nexciton energy spectrum and wave function are obtained. It is predicted that a\nweakly interacting gas of dipolar excitons in a double layer of black\nphosphorus exhibits superfluidity due to the dipole-dipole repulsion between\nthe dipolar excitons. In calculations are employed the Keldysh and Coulomb\npotentials for the interaction between the charge carriers to analyze the\ninfluence of the screening effects on the studied phenomena. It is shown that\nthe critical velocity of superfluidity, the spectrum of collective excitations,\nconcentrations of the superfluid and normal component, and mean field critical\ntemperature for superfluidity are anisotropic and demonstrate the dependence on\nthe direction of motion of dipolar excitons. The critical temperature for\nsuperfluidity increases if the exciton concentration and the interlayer\nseparation increase. It is shown that the dipolar exciton binding energy and\nmean field critical temperature for superfluidity are sensitive to the electron\nand hole effective masses. The proposed experiment to observe a directional\nsuperfluidity of excitons is addressed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Optical generation and detection of pure valley current in monolayer\n  transition metal dichalcogenides: We propose a practical scheme to generate a pure valley current in monolayer\ntransition metal dichalcogenides by one-photon absorption of linearly polarized\nlight. We show that the pure valley current can be detected by either\nphotoluminescence measurements or the ultrafast pump-probe technique. Our\nmethod, together with the previously demonstrated generation of valley\npolarization, opens up the exciting possibility of ultrafast optical-only\nmanipulation of the valley index. The tilted field effect on the valley current\nin experiment is also discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum oscillations observed in graphene at microwave frequencies: We have measured the microwave conductance of mechanically exfoliated\ngraphene at frequencies up to 8.5 GHz. The conductance at 4.2 K exhibits\nquantum oscillations, and is independent of the frequency.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Time Reversal Invariant Topologically Insulating Circuits: From studies of exotic quantum many-body phenomena to applications in\nspintronics and quantum information processing, topological materials are\npoised to revolutionize the condensed matter frontier and the landscape of\nmodern materials science. Accordingly, there is a broad effort to realize\ntopologically non-trivial electronic and photonic materials for fundamental\nscience as well as practical applications. In this work, we demonstrate the\nfirst simultaneous site- and time- resolved measurements of a time reversal\ninvariant topological band-structure, which we realize in a radio frequency\n(RF) photonic circuit. We control band-structure topology via local permutation\nof a traveling wave capacitor-inductor network, increasing robustness by going\nbeyond the tight-binding limit. We observe a gapped density of states\nconsistent with a modified Hofstadter spectrum at a flux per plaquette of\n$\\phi=\\pi/2$. In-situ probes of the band-gaps reveal spatially-localized\nbulk-states and de-localized edge-states. Time-resolved measurements reveal\ndynamical separation of localized edge-excitations into spin-polarized\ncurrents. The RF circuit paradigm is naturally compatible with non-local\ncoupling schemes, allowing us to implement a M\\\"{o}bius strip topology\ninaccessible in conventional systems. This room-temperature experiment\nilluminates the origins of topology in band-structure, and when combined with\ncircuit quantum electrodynamics (QED) techniques, provides a direct path to\ntopologically-ordered quantum matter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Domain wall motion at low current density in a synthetic antiferromagnet\n  nanowire: The current-driven motion of magnetic domain walls (DWs) is the working\nprinciple of magnetic racetrack memories. In this type of spintronic\ntechnology, high current densities are used to propel DW motion in magnetic\nnanowires, causing significant wire heating. Synthetic antiferromagnets are\nknown to show very fast DW motion at high current densities, but lower current\ndensities around onset of motion have received less attention. Here we use\nscanning transmission x-ray microscopy to study the response of DWs in a SAF\nmultilayer to currents. We observe that the DWs depin at $\\sim 3 \\times\n10^{11}$~A/m$^2$ and move more quickly in response to 5~ns duration current\npulses than in comparable conventional multilayers. The results suggest that\nDWs in SAF structures are superior to conventional N\\'{e}el DWs for low energy\nconsumption racetrack technologies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Persistent current of correlated electrons in mesoscopic ring with\n  impurity: The persistent current of correlated electrons in a continuous\none-dimensional ring with a single scatterer is calculated by solving the\nmany-body Schrodinger equation for several tens of electrons interacting via\nthe electron-electron (e-e) interaction of finite range. The problem is solved\nby the configuration-interaction (CI) and diffusion Monte Carlo (DMC) methods.\nThe CI and DMC results are in good agreement. In both cases, the persistent\ncurrent $I$ as a function of the ring length $L$ exhibits the asymptotic\ndependence $I \\propto L^{-1-\\alpha}$ typical of the Luttinger liquid, where the\npower $\\alpha$ depends only on the e-e interaction. The numerical values of\n$\\alpha$ agree with the known formula of the renormalisation-group theory.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current-induced forces in mesoscopic systems: a scattering matrix\n  approach: Nanoelectromechanical systems are characterized by an intimate connection\nbetween electronic and mechanical degrees of freedom. Due to the nanoscopic\nscale, current flowing through the system noticeably impacts the vibrational\ndynamics of the device, complementing the effect of the vibrational modes on\nthe electronic dynamics. We employ the scattering matrix approach to quantum\ntransport to develop a unified theory of nanoelectromechanical systems out of\nequilibrium. For a slow mechanical mode, the current can be obtained from the\nLandauer-B\\\"uttiker formula in the strictly adiabatic limit. The leading\ncorrection to the adiabatic limit reduces to Brouwer's formula for the current\nof a quantum pump in the absence of the bias voltage. The principal result of\nthe present paper are scattering matrix expressions for the current-induced\nforces acting on the mechanical degrees of freedom. These forces control the\nLangevin dynamics of the mechanical modes. Specifically, we derive expressions\nfor the (typically nonconservative) mean force, for the (possibly negative)\ndamping force, an effective \"Lorentz\" force which exists even for time reversal\ninvariant systems, and the fluctuating Langevin force originating from Nyquist\nand shot noise of the current flow. We apply our general formalism to several\nsimple models which illustrate the peculiar nature of the current-induced\nforces. Specifically, we find that in out of equilibrium situations the current\ninduced forces can destabilize the mechanical vibrations and cause limit-cycle\ndynamics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Microwave Experiments Simulating Quantum Search and Directed Transport\n  in Artificial Graphene: A series of quantum search algorithms have been proposed recently providing\nan algebraic speedup compared to classical search algorithms from $N$ to\n$\\sqrt{N}$, where $N$ is the number of items in the search space. In\nparticular, devising searches on regular lattices has become popular in\nextending Grover's original algorithm to spatial searching. Working in a\ntight-binding setup, it could be demonstrated, theoretically, that a search is\npossible in the physically relevant dimensions 2 and 3 if the lattice spectrum\npossesses Dirac points. We present here a proof of principle experiment\nimplementing wave search algorithms and directed wave transport in a graphene\nlattice arrangement. The idea is based on bringing localized search states into\nresonance with an extended lattice state in an energy region of low spectral\ndensity---namely, at or near the Dirac point. The experiment is implemented\nusing classical waves in a microwave setup containing weakly coupled dielectric\nresonators placed in a honeycomb arrangement, i.e., artificial graphene.\nFurthermore, we investigate the scaling behavior experimentally using linear\nchains.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "In-plane gate single-electron transistor in Ga[Al]As fabricated by\n  scanning probe lithography: A single-electron transistor has been realized in a Ga[Al]As heterostructure\nby oxidizing lines in the GaAs cap layer with an atomic force microscope. The\noxide lines define the boundaries of the quantum dot, the in-plane gate\nelectrodes, and the contacts of the dot to source and drain. Both the number of\nelectrons in the dot as well as its coupling to the leads can be tuned with an\nadditional, homogeneous top gate electrode. Pronounced Coulomb blockade\noscillations are observed as a function of voltages applied to different gates.\nWe find that, for positive top-gate voltages, the lithographic pattern is\ntransferred with high accuracy to the electron gas. Furthermore, the dot shape\ndoes not change significantly when in-plane voltages are tuned.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Plasmons in realistic graphene/hexagonal boron nitride moir\u00e9 patterns: Van der Waals heterostructures employing graphene and hexagonal boron nitride\n(hBN) crystals have emerged as a promising platform for plasmonics thanks to\nthe tunability of their collective modes with carrier density and record values\nfor plasmonics figures of merit. In this Article we investigate theoretically\nthe role of moir\\'e-pattern superlattices in nearly aligned graphene on hBN by\nusing continuum-model Hamiltonians derived from ab initio calculations. We\ncalculate the system's energy loss function for a variety of chemical potential\nvalues that are accessible in gated devices. Our calculations reveal that the\nelectron-hole asymmetry of the moir\\'e bands leads to a remarkable asymmetry of\nthe plasmon dispersion between positive and negative chemical potentials,\nshowcasing the intricate band structure and rich absorption spectrum across the\nsecondary Dirac point gap for the hole bands.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-equilibrium fractional quantum Hall states visualized by optically\n  detected MRI: Using photoluminescence microscopy enhanced by MRI, we visualize in real\nspace both electron and nuclear polarization occurring in non-equilibrium FQH\nliquids. We observe stripe-like regions comprising FQH excited states which\ndiscretely form when the FQH liquid is excited by a source-drain current. These\nregions are topologically protected and deformable, and give rise to\nbidirectionally polarized nuclear spins as spin-resolved electrons flow across\ntheir boundaries.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Directional emission of a deterministically fabricated quantum dot -\n  Bragg reflection multi-mode waveguide system: We report on the experimental study and numerical analysis of chiral\nlight-matter coupling in deterministically fabricated quantum dot (QD)\nwaveguide structures. We apply in-situ electron beam lithography to\ndeterministically integrate single InGaAs/GaAs QDs into GaAs-DBR waveguides to\nsystematically explore the dependence of chiral coupling on the position of the\nQD inside the waveguide. By a series of micro-photoluminescence measurements,\nwe determine the directionality contrast of emission into left and right\ntraveling waveguide modes revealing a maximum of 0.93 for highly off-center QDs\nand an oscillatory dependence of this contrast on the QD position. In numerical\nsimulations we obtain insight into chiral light-matter coupling by computing\nthe light field emitted by a circularly polarized source and its overlap with\nmultiple guided modes of the structure, which enables us to calculate\ndirectional $\\beta$-factors for the quantum emitters. The calculated dependence\nof the directionality on the off-center QD position is in good agreement with\nthe experimental data. It confirms the control of chiral effects in\ndeterministically fabricated QD-waveguide systems with high potential for\nfuture non-reciprocal on-chip systems required for quantum information\nprocessing.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Strong parametric coupling between two ultra-coherent membrane modes: We demonstrate parametric coupling between two modes of a silicon nitride\nmembrane. We achieve the coupling by applying an oscillating voltage to a sharp\nmetal tip that approaches the membrane surface to within a few 100 nm. When the\nvoltage oscillation frequency is equal to the mode frequency difference, the\nmodes exchange energy periodically and much faster than their free energy decay\nrate. This flexible method can potentially be useful for rapid state control\nand transfer between modes, and is an important step towards parametric spin\nsensing experiments with membrane resonators.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Room-temperature coherent optical manipulation of single-hole spins in\n  solution-grown perovskite quantum dots: Manipulation of solid-state spin coherence is an important paradigm for\nquantum information processing. Current systems either operate at very low\ntemperatures or are difficult to scale-up. Developing low-cost, scalable\nmaterials whose spins can be coherently manipulated at room temperature is thus\nhighly-attractive for a sustainable future of quantum information science. Here\nwe report ambient-condition all-optical initialization, manipulation and\nreadout of single-hole spins in an ensemble of solution-grown CsPbBr3\nperovskite QDs. Single-hole spins are obtained by sub-picosecond electron\nscavenging following a circularly-polarized femtosecond-pulse excitation. A\ntransversal magnetic field induces spin precession, and a second off-resonance\nfemtosecond-pulse coherently rotates hole spins via strong light-matter\ninteraction. These operations accomplish nearly complete quantum-state control\nof single-hole spins at room temperature.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Micromagnetic Simulation of Amorphous Ferrimagnetic TbFeCo Films with\n  Exchange Coupled Nanophases: Amorphous ferrimagnetic TbFeCo thin films are found to exhibit exchange bias\neffect near the compensation temperature by magnetic hysteresis loop\nmeasurement. The observed exchange anisotropy is believed to originate from the\nexchange interaction between the two nanoscale amorphous phases distributed\nwithin the films. Here, we present a computational model of phase-separated\nTbFeCo using micromagnetic simulation. Two types of cells with different Tb\nconcentration are distributed within the simulated space to obtain a\nheterogeneous structure consisting of two nanoscale amorphous phases. Each cell\ncontains separated Tb and FeCo components, forming two antiferromagnetically\ncoupled sublattices. Using this model, we are able to show the existence of\nexchange bias effect, and the shift in hysteresis loops is in agreement with\nexperiment. The micromagnetic model developed herein for a heterogeneous\nmagnetic material may also account for some recent measurements of exchange\nbias effect in crystalline films.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Photogalvanic effect in Weyl semimetals: We theoretically study the impact of impurities on the photogalvanic effect\n(PGE) in Weyl semimetals with weakly tilted Weyl cones. Our calculations are\nbased on a two-nodes model with an inversion symmetry breaking offset and we\nemploy a kinetic equation approach in which both optical transitions as well as\nparticle-hole excitations near the Fermi energy can be taken into account. We\nfocus on the parameter regime with a single photoactive node and control the\ncalculation in small impurity concentration. Internode scattering is treated\ngenerically and therefore our results allow to continuously interpolate between\nthe cases of short range and long range impurities. We find that the time\nevolution of the circular PGE may be nonmonotonic for intermediate internode\nscattering. Furthermore, we show that the tilt vector introduces three\nadditional linearly independent components to the steady state photocurrent.\nAmongst them, the photocurrent in direction of the tilt takes a particular role\ninasmuch it requires elastic internode scattering or inelastic intranode\nscattering to be relaxed. It may therefore be dominant. The tilt also generates\nskew scattering which leads to a current component perpendicular to both the\nincident light and the tilt. We extensively discuss our findings and comment on\nthe possible experimental implications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological Hofstadter Insulators in a Two-Dimensional Quasicrystal: We investigate the properties of a two-dimensional quasicrystal in the\npresence of a uniform magnetic field. In this configuration, the density of\nstates (DOS) displays a Hofstadter butterfly-like structure when it is\nrepresented as a function of the magnetic flux per tile. We show that the\nlow-DOS regions of the energy spectrum are associated with chiral edge states,\nin direct analogy with the Chern insulators realized with periodic lattices. We\nestablish the topological nature of the edge states by computing the\ntopological Chern number associated with the bulk of the quasicrystal. This\ntopological characterization of the non-periodic lattice is achieved through a\nlocal (real-space) topological marker. This work opens a route for the\nexploration of topological insulating materials in a wide range of non-periodic\nlattice systems, including photonic crystals and cold atoms in optical\nlattices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "True amplification of spin waves in magnonic nano-waveguides: Magnonic nano-devices exploit magnons -- quanta of spin waves -- to transmit\nand process information within a single integrated platform that has the\npotential to outperform traditional semiconductor-based electronics for low\npower applications. The main missing cornerstone of this information\nnanotechnology is an efficient scheme for the direct amplification of\npropagating spin waves. The recent discovery of spin-orbit torque provided an\nelegant mechanism for propagation losses compensation. While partial\ncompensation of the spin-wave damping has allowed for spin-wave signal\nmodulation, true amplification - the exponential increase in the spin-wave\nintensity during propagation - has so far remained elusive. Here we evidence\nthe operating conditions to achieve unambiguous amplification using clocked\nnanoseconds-long spin-orbit torque pulses in sub-micrometer wide magnonic\nwaveguides, where the effective magnetization has been engineered to be close\nto zero to suppress the detrimental magnon-magnon scattering. As a result, we\nachieve an exponential increase in the intensity of propagating spin waves up\nto 500 % at a propagation distance of several micrometers. These results pave\nthe way towards the implementation of energy efficient, cascadable magnonic\narchitectures for wave-based information processing and complex on-chip\ncomputation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Pair-wise decoherence in coupled spin qubit networks: Experiments involving phase coherent dynamics of networks of spins, such as\necho experiments, will only work if decoherence can be suppressed. We show\nhere, by analyzing the particular example of a crystalline network of Fe8\nmolecules, that most decoherence typically comes from pairwise interactions\n(particularly dipolar interactions) between the spins, which cause `correlated\nerrors'. However at very low T these are strongly suppressed. These results\nhave important implications for the design of quantum information processing\nsystems using electronic spins.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hot electrons in a tunnel structure based on metal nanoclusters: We study the effect of temperature on the tunnel current in a structure based\non gold clusters taking into consideration their discrete electronic spectra.\nWe suggest that an overheating of electron subsystem leads to the disappearance\nof a current gap and gradual smoothing of current--voltage curves that is\nobserved experimentally.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Kondo Effect in a Many-Electron Quantum Ring: The Kondo effect is investigated in a many-electron quantum ring as a\nfunction of magnetic field. For fields applied perpendicular to the plane of\nthe ring a modulation of the Kondo effect with the Aharonov-Bohm period is\nobserved. This effect is discussed in terms of the energy spectrum of the ring\nand the parametrically changing tunnel coupling. In addition, we use gate\nvoltages to modify the ground-state spin of the ring. The observed splitting of\nthe Kondo-related zero-bias anomaly in this configuration is tuned with an\nin-plane magnetic field.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-Hall Effect in A Symmetric Quantum Wells by A Random Rashba Field: Changes dopant ion concentrations in the sides of a symmetric quantum well\nare known to create a random Rashba-type spin-orbit coupling. Here we\ndemonstrate that, as a consequence, a finite size spin-Hall effect is also\npresent. Our numerical algorithm estimates the result of the Kubo formula for\nthe spin-Hall conductivity, by using a tight-binding approximation of the\nHamiltonian in the framework of a time-dependent Green's function formalism,\nwell suited for very large systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coulomb drag in graphene near the Dirac point: We study Coulomb drag in double-layer graphene near the Dirac point. A\nparticular emphasis is put on the case of clean graphene, with transport\nproperties dominated by the electron-electron interaction. Using the quantum\nkinetic equation framework, we show that the drag becomes $T$-independent in\nthe clean limit, $T\\tau \\to \\infty$, where $T$ is temperature and $1/\\tau$\nimpurity scattering rate. For stronger disorder (or lower temperature), $T\\tau\n\\ll 1/\\alpha^2$, where $\\alpha$ is the interaction strength, the kinetic\nequation agrees with the leading-order ($\\alpha^2$) perturbative result. At\nstill lower temperatures, $T\\tau \\ll 1$ (diffusive regime) this contribution\ngets suppressed, while the next-order ($\\alpha^3$) contribution becomes\nimportant; it yields a peak centered at the Dirac point with a magnitude that\ngrows with lowering $T\\tau$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Hot electron cooling by acoustic phonons in graphene: We have investigated the energy loss of hot electrons in metallic graphene by\nmeans of GHz noise thermometry at liquid helium temperature. We observe the\nelectronic temperature T / V at low bias in agreement with the heat diffusion\nto the leads described by the Wiedemann-Franz law. We report on\n$T\\propto\\sqrt{V}$ behavior at high bias, which corresponds to a T4 dependence\nof the cooling power. This is the signature of a 2D acoustic phonon cooling\nmechanism. From a heat equation analysis of the two regimes we extract accurate\nvalues of the electron-acoustic phonon coupling constant $\\Sigma$ in monolayer\ngraphene. Our measurements point to an important effect of lattice disorder in\nthe reduction of $\\Sigma$, not yet considered by theory. Moreover, our study\nprovides a strong and firm support to the rising field of graphene bolometric\ndetectors.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Micromagnetic view on ultrafast magnon generation by femtosecond spin\n  current pulses: In this Article we discuss a micromagnetic modelling approach to describe the\nultrafast spin-transfer torque excitation of coherent and incoherent magnons on\nthe nanoscale. Implementing the action of a femtosecond spin current pulse\nentering an orthogonally magnetized thin ferromagnetic film, we reproduce\nrecent experimental results and reveal the factors responsible for the unequal\nexcitation efficiency of various spin waves. Our findings are in an excellent\nagreement with the results of an analytical description of spin-wave excitation\nbased on classical kinetic equations. Furthermore, we suggest an experimental\ndesign allowing for the excitation of laterally propagating spin waves beyond\nthe optical diffraction limit. Our findings demonstrate that the classical\nmicromagnetic picture retains its predictive and interpretative power on\nfemtosecond temporal and nanometer spatial scales.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "\"Smoking gun\" signatures of topological milestones in trivial materials\n  by measurement fine-tuning and data postselection: Exploring the topology of electronic bands is a way to realize new states of\nmatter with possible implications for information technology. Because bands\ncannot always be observed directly, a central question is how to tell that a\ntopological regime has been achieved. Experiments are often guided by a\nprediction of a unique signal or a pattern, called \"the smoking gun\". Examples\ninclude peaks in conductivity, microwave resonances, and shifts in interference\nfringes. However, many condensed matter experiments are performed on relatively\nsmall, micron or nanometer-scale, specimens. These structures are in the\nso-called mesoscopic regime, between atomic and macroscopic physics, where\nphenomenology is particularly rich. In this paper, we demonstrate that the\ntrivial effects of quantum confinement, quantum interference and charge\ndynamics in nanostructures can reproduce accepted smoking gun signatures of\ntriplet supercurrents, Majorana modes, topological Josephson junctions and\nfractionalized particles. The examples we use correspond to milestones of\ntopological quantum computing: qubit spectroscopy, fusion and braiding. None of\nthe samples we use are in the topological regime. The smoking gun patterns are\nachieved by fine-tuning during data acquisition and by subsequent data\nselection to pick non-representative examples out of a fluid multitude of\nsimilar patterns that do not generally fit the \"smoking gun\" designation.\nBuilding on this insight, we discuss ways that experimentalists can rigorously\ndelineate between topological and non-topological effects, and the effects of\nfine-tuning by deeper analysis of larger volumes of data.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Liquid exfoliation of solvent-stabilised black phosphorus: applications\n  beyond electronics: Few layer black phosphorus is a new two-dimensional material which is of\ngreat interest for applications, mainly in electronics. However, its lack of\nstability severely limits our ability to synthesise and process this material.\nHere we demonstrate that high-quality, few-layer black phosphorus nanosheets\ncan be produced in large quantities by liquid phase exfoliation in the solvent\nN-cyclohexyl-2-pyrrolidone (CHP). We can control nanosheet dimensions and have\ndeveloped metrics to estimate both nanosheet size and thickness\nspectroscopically. When exfoliated in CHP, the nanosheets are remarkably stable\nunless water is intentionally introduced. Computational studies show the\ndegradation to occur by reaction with water molecules only at the nanosheet\nedge, leading to the removal of phosphorus atoms and the formation of phosphine\nand phosphorous acid. We demonstrate that liquid exfoliated black phosphorus\nnanosheets are potentially useful in a range of applications from optical\nswitches to gas sensors to fillers for composite reinforcement.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Diffusion of photo-excited holes in viscous electron fluid: The diffusion of photo-generated holes is studied in a high-mobility\nmesoscopic GaAs\\ channel where electrons exhibit hydrodynamic properties. It is\nshown that the injection of holes into such an electron system leads to the\nformation of a hydrodynamic three-component mixture consisted of electrons and\nphoto-generated heavy and light holes. The obtained results are analyzed within\nthe framework of ambipolar diffusion, which reveals characteristics of a\nviscous flow. Both hole types exhibit similar hydrodynamic characteristics. In\nsuch a way the diffusion lengths, ambipolar diffusion coefficient and the\neffective viscosity of the electron-hole system are determined.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Temperature effect in the conductance of hydrogen molecule: We present a many-body calculation for the conductance of a conducting bridge\nof a simple hydrogen molecule between $Pt$ electrodes.The experimental results\nshowed that the conductance $G=dI/dV$ has the maximum value near the quantum\nunit $G_{0}=2e^{2}/h$.\n  The $I-V$ dependence presents peak and dip and we consider that the\nelectron-phonon interaction is responsible for this behavior. At T=0 there is a\nstep in this dependence for the energy of phonons $\\omega_{0}$ which satisfies\n$eV=\\omega_{0}$. We calculated the conductance at finite temperature and showed\nthat $dG(T)/dV\\propto 1/4T\\cosh^{2}\\frac{eV-\\omega_{0}}{2T}$.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Current and Shot Noise in a Quantum Dot Coupled to Ferromagnetic Leads\n  in the Large U Limit: Using the Keldysh nonequilibrium Green function technique, we study the\ncurrent and shot noise spectroscopy of a single interacting quantum dot coupled\nto two ferromagnetic leads with different polarizations. The polarizations of\nleads can be both parallel and antiparallel alignments. General formulas of\ncurrent and shot noise are obtained, which can be applied in both the parallel\nand antiparallel alignment cases. We show that for large polarization value,\nthe differential conductance and shot noise are completely diferent for spin up\nand spin down configurations in the parallel alignment case. However, the\ndifferential conductance and shot noise have the similar properties for\nparallel alignment case in the small polarization value and for antiparallel\nalignment case in any polarization value.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron spin resonance on a 2-dimensional electron gas in a single AlAs\n  quantum well: Direct electron spin resonance (ESR) on a high mobility two dimensional\nelectron gas in a single AlAs quantum well reveals an electronic $g$-factor of\n1.991 at 9.35 GHz and 1.989 at 34 GHz with a minimum linewidth of 7 Gauss. The\nESR amplitude and its temperature dependence suggest that the signal originates\nfrom the effective magnetic field caused by the spin orbit-interaction and a\nmodulation of the electron wavevector caused by the microwave electric field.\nThis contrasts markedly to conventional ESR that detects through the microwave\nmagnetic field.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Near-Field Radiative Heat Transfer between Drift-biased Graphene through\n  Nonreciprocal Surface Plasmons: In this Rapid Communication, we theoretically demonstrate that near-field\nradiative heat transfer (NFRHT) can be modulated and enhanced by a new energy\ntransmission mode of evanescent wave, i.e. the nonreciprocal surface plasmons\npolaritons (NSPPs). In addition to the well-known coupled surface plasmon\npolaritons (SPPs), applying a drift current on a graphene sheet leads to an\nextremely asymmetric photonic transmission model, which has never been noted in\nthe noncontact heat exchanges at nanoscale before. The coupling of plasmons in\nthe infrared bands dominates the NFRHT, associated with low loss (high loss and\nultrahigh confinement) traveling along (against) the current. The dependence of\nNSPPs on the drift-current velocity as well as the vacuum gap is analyzed. It\nis found that the coupling of NSPPs at smaller and larger gap sizes exhibits\ndifferent nonreciprocities. Finally, we also demonstrate that the prominent\ninfluence of the drift current on the radiative heat flux is found at a low\nchemical potential. These findings will open a new way to spectrally control\nNFRHT, which holds great potential for improving the performance of energy\nsystems like near-field thermophotovoltaics and thermal modulator.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "What do noise measurements reveal about fractional charge in FQH\n  liquids?: We present a calculation of noise in the tunneling current through junctions\nbetween two two-dimensional electron gases (2DEG) in inequivalent Laughlin\nfractional quantum Hall (FQH) states, as a function of voltage and temperature.\nWe discuss the interpretation of measurements of suppressed shot noise levels\nof tunneling currents through a quantum point contact (QPC) in terms of\ntunneling of fractionally charged states. We show that although this\ninterpretation is always possible, for junctions between different FQH states\nthe fractionally charged states involved in the tunneling process are not the\nLaughlin quasiparticles of the isolated FQH states that make up the junction,\nand should be regarded instead as solitons of the coupled system. The charge of\nthe soliton is, in units of the electron charge, the harmonic average of the\nfilling fractions of the individual Laughlin states, which also coincides with\nthe saturation value of the differential conductance of the QPC. For the\nespecially interesting case of a QPC between states at filling fractions\n$\\nu=1$ and $\\nu={{1/3}}$, we calculate the noise in the tunneling current\nexactly for all voltages and temperatures and investigate the crossovers. These\nresults can be tested by noise experiments on $(1,{{1/3}})$ QPCs. We present a\ngeneralization of these results for QPC's of arbitrary Laughlin fractions in\ntheir weak and strong coupling regimes. We also introduce generalized Wilson\nratios for the noise in the shot and thermal limits. These ratios are universal\nscaling functions of $V/T$ that can be measured experimentally in a general QPC\ngeometry.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Sub-to-super-Poissonian photon statistics in cathodoluminescence of\n  color center ensembles in isolated diamond crystals: Impurity-vacancy centers in diamond offer a new class of robust photon\nsources with versatile quantum properties. While individual color centers\ncommonly act as single-photon sources, their ensembles have been theoretically\npredicted to have tunable photon-emission statistics. Importantly, the\nparticular type of excitation affects the emission properties of a color center\nensemble within a diamond crystal. While optical excitation favors\nnon-synchronized excitation of color centers within an ensemble, electron-beam\nexcitation can synchronize the emitters and thereby provides a control of the\nsecond-order correlation function $g_2(0)$. In this letter, we demonstrate\nexperimentally that the photon stream from an ensemble of color centers can\nexhibit $g_2(0)$ both above and below unity. Such a photon source based on an\nensemble of few color centers in a diamond crystal provides a highly tunable\nplatform for informational technologies operating at room temperature.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Field-induced dissociation of two-dimensional excitons in\n  transition-metal dichalcogenides: Generation of photocurrents in semiconducting materials requires dissociation\nof excitons into free charge carriers. While thermal agitation is sufficient to\ninduce dissociation in most bulk materials, an additional push is required to\ninduce efficient dissociation of the strongly bound excitons in monolayer\ntransition-metal dichalcogenides (TMDs). Recently, static in-plane electric\nfields have proven to be a promising candidate. In the present paper, we\nintroduce a numerical procedure, based on exterior complex scaling, capable of\ncomputing field-induced exciton dissociation rates for a wider range of field\nstrengths than previously reported in literature. We present both Stark shifts\nand dissociation rates for excitons in various TMDs calculated within the\nMott-Wannier model. Here, we find that the field induced dissociation rate is\nstrongly dependent on the dielectric screening environment. Furthermore,\napplying weak-field asymptotic theory (WFAT) to the Keldysh potential, we are\nable to derive an analytical expression for exciton dissociation rates in the\nweak-field region.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-stationary effects in the coupled quantum dots influenced by the\n  electron-phonon interaction: We analyzed time evolution of the localized charge in the system of two\ninteracting single level quantum dots (QDs) coupled with the continuous\nspectrum states in the presence of electron-phonon interaction.\n  We demonstrated that electron-phonon interaction leads to the increasing of\nlocalized charge relaxation rate. We also found that several time scales with\ndifferent relaxation rates appear in the system in the case of non-resonant\ntunneling between the dots. We revealed the formation of oscillations in the\nfilling numbers time evolution caused by the emission and adsorption processes\nof phonons.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Finite-size scaling effect on N\u00e9el temperature of antiferromagnetic\n  Cr$_2$O$_3$-(0001) films in an exchange-coupled heterostructure: The scaling of antiferromagnetic ordering temperature of corundum-type\nchromia films have been investigated. N\\'eel temperature $T_N$ was determined\nfrom the effect of perpendicular exchange-bias on the magnetization of a\nweakly-coupled adjacent ferromagnet. For a thick-film case, the validity of\ndetection is confirmed by a susceptibility measurement. Detection of $T_N$ was\npossible down to 1-nm-thin chromia films. The scaling of ordering temperature\nwith thickness was studied using different buffering materials, and compared\nwith Monte-Carlo simulations. The spin-correlation length and the corresponding\ncritical exponent were estimated, and they were consistent between experimental\nand simulation results. The spin-correlation length is an order of magnitude\nless than cubic antiferromagnets. We propose that the difference is from the\nchange of number of exchange-coupling links in the two crystal systems.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-orbit fields in asymmetric (001) quantum wells: We measure simultaneously the in-plane electron g-factor and spin relaxation\nrate in a series of undoped inversion-asymmetric (001)-oriented GaAs/AlGaAs\nquantum wells by spin-quantum beat spectroscopy. In combination the two\nquantities reveal the absolute values of both the Rashba and the Dresselhaus\ncoefficients and prove that the Rashba coefficient can be negligibly small\ndespite huge conduction band potential gradients which break the inversion\nsymmetry. The negligible Rashba coefficient is a consequence of the\n'isomorphism' of conduction and valence band potentials in quantum systems\nwhere the asymmetry is solely produced by alloy variations.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dirac-point engineering and topological phase transitions in honeycomb\n  optical lattices: We study the electronic structure and the phase diagram of non-interacting\nfermions confined to hexagonal optical lattices. In the first part, we compare\nthe properties of Dirac points arising in the eigenspectrum of either honeycomb\nor triangular lattices. Numerical results are complemented by analytical\nequations for weak and strong confinements. In the second part we discuss the\nphase diagram and the evolution of Dirac points in honeycomb lattices applying\na tight-binding description with arbitrary nearest-neighbor hoppings. With\nincreasing asymmetry between the hoppings the Dirac points approach each other.\nAt a critical asymmetry the Dirac points merge to open an energy gap, thus\nchanging the topology of the eigenspectrum. We analyze the trajectory of the\nDirac points and study the density of states in the different phases.\nManifestations of the phase transition in the temperature dependence of the\nspecific heat and in the structure factor are discussed.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Shot noise of series quantum point contacts intercalating chaotic\n  cavities: Shot noise of series quantum point contacts forming a sequence of cavities in\na two dimensional electron gas are studied theoretically and experimentally.\nNoise in such a structure originates from local scattering at the point\ncontacts as well as from chaotic motion of the electrons in the cavities. We\nfound that the measured shot noise is in reasonable agreement with our\ntheoretical prediction taking the cavity noise into account.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Giga-Hertz quantized charge pumping in bottom gate defined InAs nanowire\n  quantum dots: Semiconducting nanowires (NWs) are a versatile, highly tunable material\nplatform at the heart of many new developments in nanoscale and quantum\nphysics. Here, we demonstrate charge pumping, i.e., the controlled transport of\nindividual electrons through an InAs NW quantum dot (QD) device at frequencies\nup to $1.3\\,$GHz. The QD is induced electrostatically in the NW by a series of\nlocal bottom gates in a state of the art device geometry. A periodic modulation\nof a single gate is enough to obtain a dc current proportional to the frequency\nof the modulation. The dc bias, the modulation amplitude and the gate voltages\non the local gates can be used to control the number of charges conveyed per\ncycle. Charge pumping in InAs NWs is relevant not only in metrology as a\ncurrent standard, but also opens up the opportunity to investigate a variety of\nexotic states of matter, e.g. Majorana modes, by single electron spectroscopy\nand correlation experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Analytical description of the 1s exciton linewidth\n  temperature-dependence in transition metal dichalcogenides: We obtain an analytical expression for the linewidth of the 1s-exciton as a\nfunction of temperature in transition metal dichalcogenides. The total\nlinewidth, as function of temperature, is dominated by three contributions: (i)\nthe radiative decay (essentially temperature independent); (ii) the\nphonon-induced intravalley scattering; (iii) the phonon-induced intervalley\nscattering. Our approach uses a variational \\emph{Ansatz} to solve the Wannier\nequation allowing for an analytical treatment of the excitonic problem,\nincluding rates of the decay dynamics. Our results are in good agreement with\nexperimental data already present in the literature and can be used to readily\npredict the value of the total linewidth at any temperature in the broad class\nof excitonic two-dimensional materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological Number of Edge States: We show that the edge states of the four-dimensional class A system can have\ntopological charges, which are characterized by Abelian/non-Abelian monopoles.\nThe edge topological charges are a new feature of relations among theories with\ndifferent dimensions. From this novel viewpoint, we provide a non-Abelian\nanalogue of the TKNN number as an edge topological charge, which is defined by\nan SU(2) 't Hooft-Polyakov BPS monopole through an equivalence to Nahm\nconstruction. Furthermore, putting a constant magnetic field yields an edge\nmonopole in a non-commutative momentum space, where D-brane methods in string\ntheory facilitate study of edge fermions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Controllable Spin-Transfer Torque on an Antiferromagnet in a Dual\n  Spin-Valve: We consider current-induced spin-transfer torque on an antiferromagnet in a\ndual spin-valve setup. It is demonstrated that a net magnetization may be\ninduced in the AFM by partially or completely aligning the sublattice\nmagnetizations via a current-induced spin-transfer torque. This effect occurs\nfor current densities ranging below 10$^6$ A/cm$^2$. The direction of the\ninduced magnetization in the AFM is shown to be efficiently controlled by means\nof the magnetic configuration of the spin-valve setup, with the anti-parallell\nconfiguration yielding the largest spin-transfer torque. Interestingly, the\nmagnetization switching time-scale $\\tau_\\text{switch}$ itself has a strong,\nnon-monotonic dependence on the spin-valve configuration. These results may\npoint toward new ways to incorporate AFMs in spintronic devices in order to\nobtain novel types of functionality.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Signatures of spin-orbit coupling in scanning gate conductance images of\n  electron flow from quantum point contacts: Electron flow through a quantum point contact in presence of spin-orbit\ncoupling is investigated theoretically in the context of the scanning gate\nmicroscopy (SGM) conductance mapping. Although in the absence of the floating\ngate the spin-orbit coupling does not significantly alter the conductance, we\nfind that the angular dependence of the SGM images of the electron flow at the\nconductance plateaux is substantially altered as the spin-orbit interaction\nmixes the orbital modes that enter the quantum point contact. The radial\ninterference fringes that are obtained in the SGM maps at conductance steps are\nessentially preserved by the spin-orbit interaction as backscattering by the\ntip preserves the electron spin although the effects of the mode mixing are\nvisible.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Probing the potential landscape inside a two-dimensional electron-gas: We report direct observations of the scattering potentials in a\ntwo-dimensional electron-gas using electron-beam diffaction-experiments. The\ndiffracting objects are local density-fluctuations caused by the spatial and\ncharge-state distribution of the donors in the GaAs-(Al,Ga)As heterostructures.\nThe scatterers can be manipulated externally by sample illumination, or by\ncooling the sample down under depleted conditions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mechanism for self-formation of periodic structures on a plastic polymer\n  surface using a nanosecond and femtosecond laser pulses: The high UV laser dose at 193 nm induces grooves on poly allyl diglycol\ncarbonate PADC (CR39) at normal irradiation. The spatial period exhibits to be\nnearly invariant for azimuth and polar angles indicating a loose dependence on\nthe incident angles but the LIPSS (Laser-induced periodic surface structures)\nare always parallel to the P polarization component of the incident beam. The\nmost common approach to explain LIPSS formation is related to the Sipe theory\nwhich does not account for all the observed phenomena especially LIPSS with\nperiodicity larger than the laser wavelength. In fact the LIPSS is a multi\nparameter mechanism based on surface rippling, acoustic modulation and laser\nablation and etc. In experiment with CR-39 polymer, laser irradiation produce a\nvery tiny melting layer of mixture of monomer due to depolymerization on the\nsurface and it seems capillary wave is responsible for grooves formation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Control of Plasmons in Topological Insulators via Local Perturbations: We use a fully quantum mechanical approach to demonstrate control of\nplasmonic excitations in prototype models of topological insulators by\nmolecule-scale perturbations. Strongly localized surface plasmons are present\nin the host systems, arising from the topologically non-trivial single-particle\nedge states. A numerical evaluation of the RPA equations for the perturbed\nsystems reveals how the positions and the internal electronic structure of the\nadded molecules affect the degeneracy of the locally confined collective\nexcitations, i.e., shifting the plasmonic energies of the host system and\nchanging their spatial charge density profile. In particular, we identify\nconditions under which significant charge transfer from the host system to the\nadded molecules occurs. Furthermore, the induced field energy density in the\nperturbed topological systems due to external electric fields is determined.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "One-Dimensional Luttinger Liquids in a Two-Dimensional Moir\u00e9 Lattice: The Luttinger liquid (LL) model of one-dimensional (1D) electronic systems\nprovides a powerful tool for understanding strongly correlated physics\nincluding phenomena such as spin-charge separation. Substantial theoretical\nefforts have attempted to extend the LL phenomenology to two dimensions (2D),\nespecially in models of closely packed arrays of 1D quantum wires, each being\ndescribed as a LL. Such coupled-wire models have been successfully used to\nconstruct 2D anisotropic non-Fermi liquids, quantum Hall states, topological\nphases, and quantum spin liquids. However, an experimental demonstration of\nhigh-quality arrays of 1D LLs suitable for realizing these models remains\nabsent. Here we report the experimental realization of 2D arrays of 1D LLs with\ncrystalline quality in a moir\\'e superlattice made of twisted bilayer tungsten\nditelluride (tWTe$_{2}$). Originating from the anisotropic lattice of the\nmonolayer, the moir\\'e pattern of tWTe$_{2}$ hosts identical, parallel 1D\nelectronic channels, separated by a fixed nanoscale distance, which is tunable\nby the interlayer twist angle. At a twist angle of ~ 5 degrees, we find that\nhole-doped tWTe$_{2}$ exhibits exceptionally large transport anisotropy with a\nresistance ratio of ~ 1000 between two orthogonal in-plane directions. The\nacross-wire conductance exhibits power-law scaling behaviors, consistent with\nthe formation of a 2D anisotropic phase that resembles an array of LLs. Our\nresults open the door for realizing a variety of correlated and topological\nquantum phases based on coupled-wire models and LL physics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous Nernst effect and field-induced Lifshitz transition in Weyl\n  semimetals TaP and TaAs: The discovery of Weyl fermions in transition metal monoarsenides/phosphides\nwithout inversion symmetry represents an exceptional breakthrough in modern\ncondensed matter physics. However, exploring the inherent nature of these\nquasiparticles is experimentally elusive because most of the experimental\nprobes rely on analysing Fermi arc topology or controversial signatures such as\nthe appearance of the chiral anomaly and the giant magnetoresistance. Here we\nshow that the prototypical type-I Weyl semimetals TaP and TaAs possess a giant\nanomalous Nernst signal with a characteristic saturation plateau beyond a\ncritical field which can be understood as a direct consequence of the finite\nBerry curvature originating from the Weyl points. Our results thus promote the\nNernst coefficient as an ideal bulk probe for detecting and exploring the\nfingerprints of emergent Weyl physics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunnel magnetoresistance and temperature related effects in magnetic\n  tunnel junctions with embedded nanoparticles: Temperature dependence of the tunnel magnetoresistance (TMR) was calculated\nin range of the quantum-ballistic model in the magnetic tunnel junctions (MTJs)\nwith embedded nanoparticles (NPs). The electron tunnel transport through NP was\nsimulated in range of double barrier approach, which was integrated into the\nmodel of the magnetic point-like contact. The resonant TMR conditions and\ntemperature impact were explored in detail. Moreover, the possible reasons of\nthe temperature induced resonant conditions were discussed in the range of the\nlead-tunneling cell-lead model near Kondo temperature. We also found that\nredistribution of the voltage drop becomes crucial in this model. Furthermore,\nthe direct tunneling plays the dominant role and cannot be omitted in the\nquantum systems with the total tunneling thickness up to 5-6 nm. Hence, Coulomb\nblockade model cannot explain Kondo-induced TMR anomalies in nanometer-sized\ntunnel junctions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Compensation of the Kondo effect in quantum dots coupled to\n  ferromagnetic leads within equation of motion approach: We propose a new approximation scheme within equation of motion approach\n(EOM) to spin polarized transport through a quantum dot coupled to\nferromagnetic leads. It has some advantages over a widely used in the\nliterature standard EOM technique, in particular when we are interested in spin\npolarized quantities. Namely, it gives the values of the dot spin polarization\nwhich are closer to the ones obtained within numerical renormalization group\n(NRG), than the standard EOM approach. While restoring the Kondo effect, the\nspin polarization vanishes and the transport becomes unpolarized, in agreement\nwith NRG and a real time diagrammatic calculations. The standard EOM procedure\ngives nonzero values of the spin polarization, and the transport is still spin\npolarized. Both approximations give the same correct splitting of the Kondo\npeaks due to ferromagnetism in the electrodes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Semiconductor quantum well irradiated by a two-mode electromagnetic\n  field as a terahertz emitter: We study theoretically the nonlinear optical properties of a semiconductor\nquantum well (QW) irradiated by a two-mode electromagnetic wave consisting of a\nstrong resonant dressing field and a weak off-resonant driving field. In the\nconsidered strongly coupled electron-field system, the dressing field opens\ndynamic Stark gaps in the electron energy spectrum of the QW, whereas the\ndriving field induces electron oscillations in the QW plane. Since the gapped\nelectron spectrum restricts the amplitude of the oscillations, the emission of\na frequency comb from the QW appears. Therefore, the doubly-driven QW operates\nas a nonlinear optical element which can be used, particularly, for optically\ncontrolled generation of terahertz radiation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Mapping Spin Interactions from Conductance Peak Splitting in Coulomb\n  Blockade: We investigate the transport properties of a quantum dot coupled to leads\ninteracting with a multi-spin system using the generalized master equation\nwithin the Coulomb blockade regime. We find that if two states for each\nscattering region electron manifold are included, several signatures of the\ninteracting spin system appear in steady-state transport properties. We provide\na theoretical mapping of differential conductance peak signatures and all spin\nHamiltonian parameters related to the inclusion of excited state transitions\nbetween uncharged and charged electron manifolds. Our predictions describe a\nscheme of only using a quantum dot and differential conductance to measure\nmagnetic anisotropy, inter-spin exchange coupling, exchange coupling between\nthe spin system and itinerant electron, and applied magnetic field response.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "A simple view on the quantum Hall system: The physics of the quantum Hall system becomes very simple when studied on a\nthin torus. Remarkably, however, the very rich structure still exists in this\nlimit and there is a continuous route to the bulk system. Here we review recent\nprogress in understanding various features of the quantum Hall system in terms\nof a simple one-dimensional model corresponding to the thin torus.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin waves in zigzag graphene nanoribbons and the stability of edge\n  ferromagnetism: We study the low energy spin excitations of zigzag graphene nanoribbons of\nvarying width. We find their energy dispersion at small wave vector to be\ndominated by antiferromagnetic correlations between the ribbon's edges, in\naccrodance with previous calculations. We point out that spin wave lifetimes\nare very long due to the semi-conducting nature of the electrically neutral\nnanoribbons. However, application of very modest gate voltages cause a\ndiscontinuous transition to a regime of finite spin wave lifetime. By further\nincreasing doping the ferromagnetic alignments along the edge become unstable\nagainst transverse spin fluctuations. This makes the experimental detection of\nferromagnetism is this class of systems very delicate, and poses a difficult\nchallenge to the possible uses of these nanoribbons as basis for spintronic\ndevices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Saturation and bistability of defect-mode intersubband polaritons: In this article we report about linear and nonlinear optical properties of\nintersubband cavity polariton samples, where the resonant photonic mode is a\ndefect state in a metallo-dielectric photonic crystal slab. By tuning a single\ngeometric parameter of the resonator, the cavity Q-factor can reach values as\nlarge as 85, with a consequent large cooperativity for the light-matter\ninteraction. We show that a device featuring large cooperativity leads to sharp\nsaturation, or even bistability, of the polariton states. This nonlinear\ndynamics occurs at the crossover between the weak and the strong coupling\nregimes, where the weak critical coupling concept plays a fundamental role.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ligand effects on the electronic structure and magnetism of magnetite\n  surfaces: We address the effect of functionalization on the electronic and magnetic\nproperties of magnetite surface as an indicator of the same properties in\nnanoparticles too big for a direct ab-initio approach. Using well-established\nmethods and references (namely LDA+U on magnetite surfaces) we could verify the\nvalidity of our approach, and using two typical ligands, dopamine and citrate,\nnamely pi and sigma electron donors, we could predict that those ligands would\ninduce a different change in the electronic properties of the systems, but in\nboth cases an enhancement of magnetization.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "High temperature magnetism and microstructure of semiconducting\n  ferromagnetic alloy (GaSb)$_{1-x}$(MnSb)$_{x}$: We have studied the properties of relatively thick (about 120 nm) magnetic\ncomposite films grown by pulsed laser deposition method using\n(GaSb)$_{0.59}$(MnSb)$_{0.41}$ eutectic compound as a target for sputtering.\nFor the studied films we have observed ferromagnetism and anomalous Hall effect\nabove the room temperature, it manifests the presence of spin-polarized\ncarriers. Electron microscopy, atomic and magnetic force microscopy results\nsuggests that films under study have homogenous columnar structure in the bulk\nwhile MnSb inclusions accumulate near it's surface. This is in good agreement\nwith high mobility values of charge carriers. Based on our data we conclude\nthat room temperature magnetic and magnetotransport properties of the films are\ndefined by MnSb inclusions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Coherent Multielectron Processes in an Atomic Scale Contact: The light emission from a scanning tunneling microscope operated on a Ag(111)\nsurface at 6 K is analyzed from low conductances to values approaching the\nconductance quantum. Optical spectra recorded at a sample voltages V reveal\nemission with photon energies hv> 2eV. A model of electrons interacting\ncoherently via a localized plasmon-polariton mode reproduces the experimental\ndata, in particular the kinks in the spectra at eV and 2eV as well as the\nscaling of the intensity at low and intermediate conductances.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous Spin Dephasing in (110) GaAs Quantum Wells: Anisotropy and\n  Intersubband Effects: A strong anisotropy of electron spin decoherence is observed in GaAs/(AlGa)As\nquantum wells grown on (110) oriented substrate. The spin lifetime of spins\nperpendicular to the growth direction is about one order of magnitude shorter\ncompared to spins along (110). The spin lifetimes of both spin orientations\ndecrease monotonically above a temperature of 80 and 120 K, respectively. The\ndecrease is very surprising for spins along (110) direction and cannot be\nexplained by the usual Dyakonov Perel dephasing mechanism. A novel spin\ndephasing mechanism is put forward that is based on scattering of electrons\nbetween different quantum well subbands.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "On the nature of the spin polarization limit in the warped Dirac cone of\n  the Bi2Te3: The magnitude of electron spin polarization in topologically protected\nsurface states is an important parameter with respect to spintronics\napplications. In order to analyze the warped spin texture in Bi$_2$Te$_3$ thin\nfilms, we combine angle- and spin-resolved photoemission experiments with\ntheoretical \\textit{ab initio} calculations. We find an \\textit{in-plane} spin\npolarization of up to $\\sim$~45\\% in the topologically protected Dirac cone\nstates near the Fermi level. The Fermi surface of the Dirac cone state is\nwarped and shows an \\textit{out-of-plane} spin polarization of $\\sim$~15\\%.\nThese findings are in quantitative agreement with dedicated simulations which\nfind electron density of the Dirac cone delocalized over the first quintuple\nlayer with spin reversal occurring in the surface atomic layer.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Vorticity and quantum turbulence in the merging of superfluid Helium\n  nanodroplets: We have studied the merging of two $^4$He droplets at zero temperature,\ncaused by their Van der Waals mutual attraction. During the early stages of the\nmerging, density structures appear which closely match the experimental\nobservations by Vicente et al. [J. Low Temp. Phys. 121, 627 (2000)]. When the\ndroplets are merging, quantized vortex-antivortex ring pairs nucleate at the\nsurface and annihilate inside the merged droplet producing a roton burst. We\nalso observe the nucleation of quantized vortex-antivortex rings that wrap the\ndroplet surface and remain localized on the surface until they eventually decay\ninto short-wavelength surface waves. Analysis of the kinetic energy spectrum\ndiscloses the existence of a regime where turbulence caused by vortex\ninteraction and annihilation is characterized by a Kolmogorov power law. This\nis followed by another regime where roton radiation (produced by\nvortex-antivortex annihilation) dominates, whose hallmark is a weak, turbulent\nsurface dynamics. We suggest that similar processes might appear in superfluid\nhelium droplets after they capture impurities or if they are produced by\nhydrodynamic instability of a liquid jet. Experiments on collisions between\nrecently-discovered self-bound Bose-Einstein condensates should display a\nsimilar phenomenology.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Voltage switching and domain relocation in semiconductor superlattices: A numerical study of domain wall relocation during voltage switching with\ndifferent ramping times is presented for weakly coupled, doped semiconductor\nsuperlattices exhibiting multistable domain formation in the first plateau of\ntheir current-voltage characteristics. Stable self-oscillations of the current\nat the end of stable stationary branches of the current-voltage characteristics\nhave been found. These oscillations are due to periodic motion of charge\ndipoles near the cathode that disappear inside the SL, before they can reach\nthe receiving contact. Depending on the dc voltage step, the type of\nmultistability between static branches and the duration of voltage switching,\nunusual relocation scenarios are found including changes of the current that\nfollow adiabatically the stable I--V branches, different faster episodes\ninvolving charge tripoles and dipoles, and even small amplitude oscillations of\nthe current near the end of static I--V branches followed by dipole-tripole\nscenarios.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Metastability and dynamics in remanent states of square artificial spin\n  ice with long-range dipole interactions: After removal of an applied magnetic field, artificial square spin ice can be\nleft in a metastable remanent state, with nonzero residual magnetization and\nexcess energy above the ground state. Using a model of magnetic islands with\ndipoles of fixed magnitude and local anisotropies, the remanent states are\nprecisely determined here, including all long-range dipole interactions. Small\ndeviations away from remanent states are analyzed and the frequencies of modes\nof oscillation are determined. Some modes reach zero frequency at high symmetry\nwave vectors, such that the stability limits are found, as determined by the\nlocal anisotropy strength relative to the dipolar coupling strength.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Periodic negative differential conductance in a single metallic\n  nano-cage: We report a bi-polar multiple periodic negative differential conductance\n(NDC) effect on a single cage-shaped Ru nanoparticle measured using scanning\ntunneling spectroscopy. This phenomenon is assigned to the unique\nmultiply-connected cage architecture providing two (or more) defined routes for\ncharge flow through the cage. This, in turn, promotes a self- gating effect,\nwhere electron charging of one route affects charge transport along a\nneighboring channel, yielding a series of periodic NDC peaks. This picture is\nestablished and analyzed here by a theoretical model.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermally-Activated Phase Slips in Superfluid Spin Transport in Magnetic\n  Wires: We theoretically study thermally-activated phase slips in superfluid spin\ntransport in easy-plane magnetic wires within the stochastic\nLandau-Lifshitz-Gilbert phenomenology, which runs parallel to the\nLanger-Ambegaokar-McCumber-Halperin theory for thermal resistances in\nsuperconducting wires. To that end, we start by obtaining the exact solutions\nfor free-energy minima and saddle points. We provide an analytical expression\nfor the phase-slip rate in the zero spin-current limit, which involves detailed\nanalysis of spin fluctuations at extrema of the free energy. An experimental\nsetup of a magnetoeletric circuit is proposed, in which thermal phase slips can\nbe inferred by measuring nonlocal magnetoresistance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Critical current of spin transfer torque-driven magnetization dynamics\n  in magnetic multilayers: The critical current of the spin transfer torque-driven magnetization\ndynamics was studied by taking into account both spin pumping and the finite\npenetration depth of the transverse spin current. We successfully reproduced\nthe recent experimental results obtained by Chen et al. [Phys. Rev. B {\\bf 74},\n144408 (2006)] and found that the critical current remains finite even in the\nzero-thickness limit of the free layer. We showed that the remaining value of\nthe critical current is determined mainly by spin pumping.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-equilibrium theory for strongly coupled quantum dot with arbitrary\n  on-site correlation strength: An analytical expression for the current through a single level quantum dot\nfor arbitrary strength of the on-site electron-electron interaction is derived\nbeyond standard mean-field theory. By describing the localised states in terms\nof many-body operators, the employed diagrammatic technique for strong coupling\nenables inclusion of electron correlation effects into the description of the\nlocal dynamics, which provides transport properties that are consistent with\nrecent experimental data.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spin-Torque and Spin-Hall Nano-Oscillators: This paper reviews the state of the art in spin-torque and spin Hall effect\ndriven nano-oscillators. After a brief introduction to the underlying physics,\nthe authors discuss different implementations of these oscillators, their\nfunctional properties in terms of frequency range, output power, phase noise,\nand modulation rates, and their inherent propensity for mutual synchronization.\nFinally, the potential for these oscillators in a wide range of applications,\nfrom microwave signal sources and detectors to neuromorphic computation\nelements, is discussed together with the specific electronic circuitry that has\nso far been designed to harness this potential.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Persistent currents and magnetic flux trapping in fragments of carbon\n  deposits containing multiwalled nanotubes: It is found that the magnetization curves of samples of fragments of cathode\ncarbon deposits with a high content of multiwalled nanotubes exhibit a\npronounced irreversible character, attesting to the induction of persistent\ncurrents in the samples and to magnetic flux trapping, as happens in a multiply\nconnected superconducting structure. A decrease of the trapped flux in time\ncould not be observed at low (helium) temperatures with a measurement time of\nabout 20 h. For intermediate (~30K) and room temperatures the trapped magnetic\nflux decays slowly with characteristic relaxation times of the order of 150 and\n15 h, respectively.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Geometrical Effect Explains Graphene Membrane Stiffening at Finite\n  Vacancy Concentrations: The presence of defects such as vacancies in solids has prominent effects on\ntheir mechanical properties. It not only modifies the stiffness and strength of\nmaterials, but also changes their morphologies. The latter effect is extremely\nsignificant for low- dimensional materials such as graphene. We show in this\nwork that graphene swells while point defects such as vacancies are created at\nfinite concentrations. The distorted geometry resulted from this areal\nexpansion, in combination with the in-plane softening effect, predicts an\nunusual defect concentration dependence of stiffness measured for supported\ngraphene membrane in nanoindentation tests, which explains the defect- induced\nstiffening phenomenon reported recently. The mechanism is elucidated through an\nanalytical membrane model as well as numerical simulations at atomistic and\ncontinuum levels. In addition to elucidate the counter-intuitive observations\nin experiments and computer simulations, our findings also highlight the role\nof defect- modulated morphology engineering that can be quite effective in\ndesigning nanoscale material and structural applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The Atomic and Electronic structure of 0\u00b0 and 60\u00b0 grain\n  boundaries in MoS2: We have investigated atomic and electronic structure of grain boundaries in\nmonolayer MoS2, where relative angles between two different grains are 0 and 60\ndegree. The grain boundaries with specific relative angle have been formed with\nchemical vapor deposition growth on graphite and hexagonal boron nitride\nflakes; van der Waals interlayer interaction between MoS2 and the flakes\nrestricts the relative angle. Through scanning tunneling microscopy and\nspectroscopy measurements, we have found that the perfectly stitched structure\nbetween two different grains of MoS2 was realized in the case of the 0 degree\ngrain boundary. We also found that even with the perfectly stitched structure,\nvalence band maximum and conduction band minimum shows significant blue shift,\nwhich probably arise from lattice strain at the boundary.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "On the Relevance of Disorder for Dirac Fermions with Imaginary Vector\n  Potential: We consider the effects of disorder in a Dirac-like Hamiltonian. In order to\nuse conformal perturbation theory, we argue that one should consider disorder\nin an imaginary vector potential. This affects significantly the signs of the\nlowest order $\\beta$eta functions. We present evidence for the existence of two\ndistinct universality classes, depending on the relative strengths of the gauge\nfield verses impurity disorder strengths. In one class all disorder is driven\nirrelevant by the gauge field disorder.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Kinetic Monte Carlo Approach to Non-equilibrium Bosonic Systems: We consider the use of a Kinetic Monte Carlo approach for the description of\nnon-equilibrium bosonic systems, taking non-resonantly excited\nexciton-polariton condensates and bosonic cascade lasers as examples. In the\nformer case, the considered approach allows the study of the cross-over between\nincoherent and coherent regimes, which represents the formation of a\nquasi-condensate that forms purely from the action of energy relaxation\nprocesses rather than interactions between the condensing particles themselves.\nIn the latter case, we show that a bosonic cascade can theoretically develop an\noutput coherent state.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Non-adiabatic current generation in a finite width semiconductor ring: We consider a model of a semiconductor quantum ring of finite width in a\nconstant perpendicular magnetic field. We show how a current of the same order\nas the persistent current can be generated non-adiabatically by a short\nintensive pulse in the Tera-Hertz regime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum gates by periodic driving: Topological quantum computation has been extensively studied due to its\nrobustness against decoherence. A conventional way to realize it is by\nadiabatic operations---it requires relatively long time to accomplish so that\nthe speed of quantum computation slows down. In this work, we present a method\nto realize topological quantum computation by periodic driving. Compared to the\nadiabatic evolution, the total operation time can be regulated arbitrarily by\nthe amplitude and frequency of the periodic driving. For the sinusoidal\ndriving, we give an expression for the total operation time in the\nhigh-frequency limit. For the square wave driving, we derive an exact\nanalytical expression for the evolution operator without any approximations,\nand show that the amplitude and frequency of driving field depend on its period\nand total operation time. This could provide a new direction in regulations of\nthe operation time in topological quantum computation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Microscopic theory of quantum-transport phenomena in mesoscopic systems:\n  A Monte Carlo approach: A theoretical investigation of quantum-transport phenomena in mesoscopic\nsystems is presented. In particular, a generalization to ``open systems'' of\nthe well-known semiconductor Bloch equations is proposed. The presence of\nspatial boundary conditions manifest itself through self-energy corrections and\nadditional source terms in the kinetic equations, whose form is suitable for a\nsolution via a generalized Monte Carlo simulation. The proposed approach is\napplied to the study of quantum-transport phenomena in double-barrier\nstructures as well as in superlattices, showing a strong interplay between\nphase coherence and relaxation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Voltage-Controlled Low-Energy Switching of Nanomagnets through\n  Ruderman-Kittel-Kasuya-Yosida Interactions for Magnetoelectric Device\n  Applications: In this letter, we consider through simulation Ruderman-Kittel-Kasuya-Yosida\n(RKKY) interactions between nanomagnets sitting on a conductive surface, and\nvoltage-controlled gating thereof for low-energy switching of nanomagnets for\npossible memory and nonvolatile logic applications. For specificity, we\nconsider nanomagnets with perpendicular anisotropy on a three-dimensional\ntopological insulator. We model the possibility and dynamics of RKKY-based\nswitching of one nanomagnet by coupling to one or more nanomagnets of set\norientation. Applications for both memory and nonvolatile logic are considered,\nwith follower, inverter and majority gate functionality shown. Sub-attojoule\nswitching energies, far below conventional spin transfer torque (STT)-based\nmemories and even below CMOS logic appear possible. Switching times on the\norder of a few nanoseconds, comparable to times for STT switching, are\nestimated for ferromagnetic nanomagnets.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Photon Absorption of Two-dimensional Nonsymmorphic Dirac Semimetals: Two-dimensional Dirac semimetals have attracted much attention because of\ntheir linear energy dispersion and non-trivial Berry phase. Graphene-like 2D\nDirac materials are gapless only within certain approximations, e.g., if\nspin-orbit coupling (SOC) is neglected. It has recently been reported that\nmaterials with nonsymmorphic crystal lattice possess symmetry-enforced\nDirac-like band dispersion around certain high-symmetry momenta even in the\npresence of SOC. Here we calculate the optical absorption coefficient of\nnonsymmorphic semimetals, such as $\\alpha$-bismuthene, which hosts two\nanisotropic Dirac cones with different Fermi velocities along $x$ and $y$\ndirections.We find that the optical absorption coefficient depends strongly on\nthe anisotropy factor and the photon polarization. When a magnetic field is\napplied perpendicular to the plane of the material, the absorption coefficient\nalso depends on an internal parameter we termed the mixing angle of the band\nstructure. We further find that an in-plane magnetic field, while leaving the\nsystem gapless, can induce a Van-Hove singularity in the joint density of\nstates: this causes a significant enhancement of the optical absorption at the\nfrequency of the singularity for one direction of polarization but not for the\northogonal one, making the optical properties even more strongly dependent on\npolarization. Due to the anisotropy present in our model, the Dirac cones at\ntwo high-symmetry momenta in the Brillouin zone contribute very differently to\nthe optical absorbance. Consequently, it might be possible to preferentially\npopulate one valley or the other by varying photon polarization and frequency.\nThese results suggest that nonsymmorphic 2D Dirac semimetals are excellent\ncandidate materials for tunable magneto-optic devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Surface segregation in nanoparticles from first principles: FePt nanoparticles are known to exhibit reduced L1$_0$ order with decreasing\nparticle size. The reduction in order reduces the magnetic anisotropy and the\nthermal stability of the direction of magnetization of the particle. The\nphenomenon is addressed by investigating the thermodynamic driving forces for\nsurface segregation using a local (inhomogeneous) cluster expansion fitted to\nab initio data which accurately represents interatomic interactions in both the\nbulk and surface regions. Subsequent Monte Carlo simulations reveal that first\nsurface layer Pt segregation is compensated by Pt depletion in the second\nsubsurface layer. This indicates that the core's ordered state is not affected\nby surface thermodynamics as much as previously thought. Thus, the weak\nordering experimentally observed is likely not due to fundamental thermodynamic\nlimitations but rather to kinetic effects.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Deterministic formation of highly coherent nitrogen-vacancy centers\n  using a focused electron irradiation technique: We demonstrate fully three-dimensional and patterned localization of\nnitrogen-vacancy (NV) centers in diamond with coherence times in excess of 1\nms. Nitrogen {\\delta}-doping during CVD diamond growth vertically confines\nnitrogen to 4 nm while electron irradiation with a transmission electron\nmicroscope (TEM) laterally confines vacancies to less than 1 {\\mu}m. We\ncharacterize the effects of electron energy and dose on NV formation.\nImportantly, our technique enables the formation of reliably high-quality NV\ncenters inside diamond nanostructures, with applications in quantum information\nand sensing.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magneto-Electric Effect for Multiferroic Thin Film by Monte Carlo\n  Simulation: Magneto-electric effect in a multiferroic heterostructure film, i.e. a\ncoupled ferromagnetic-ferroelectric thin film, has been investigated through\nthe use of the Metropolis algorithm in Monte Carlo simulations. A classical\nHeisenberg model describes the energy stored in the ferromagnetic film, and we\nuse a pseudo-spin model with a transverse Ising Hamiltonian to characterise the\nenergy of electric dipoles in the ferroelectric film. The purpose of this\narticle is to demonstrate the dynamic response of polarisation is driven by an\nexternal magnetic field, when there is a linear magneto-electric coupling at\nthe interface between the ferromagnetic and ferroelectric components.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effect of laser on thermopower of chiral carbon nanotube: An investigation of laser stimulated thermopower in chiral CNT is presented.\nThe thermopower of a chiral CNT is calculated using a tractable analytical\napproach. This is done by solving the Boltzmann kinetic equation with energy\ndispersion relation obtained in the tight binding approximation to determine\nthe electrical and thermal properties of chiral carbon nanotubes. The\ndifferential thermoelectric power {\\alpha} along the circumferential and axial\naxes are obtained. The results obtained are numerically analyzed and {\\alpha}\nis found to oscillate in the presence of laser radiations. We have also noted\nthat Laser source above 4.6 x 107V/m lowered the thermopower otherwise there is\nno change. Varying delta s and delta z the thermopower changes from positive to\nnegative.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Excited State Quantum Couplings and Optical Switching of an Artificial\n  Molecule: We optically probe the spectrum of ground and excited state transitions of an\nindividual, electrically tunable self-assembled quantum dot molecule.\nPhotocurrent absorption measurements show that the spatially direct neutral\nexciton transitions in the upper and lower dots are energetically separated by\nonly ~2 meV. Excited state transitions ~8-16 meV to higher energy exhibit\npronounced anticrossings as the electric field is tuned due to the formation of\nhybridized electron states. We show that the observed excited state transitions\noccur between these hybridized electronic states and different hole states in\nthe upper dot. By simultaneously pumping two different excited states with two\nlaser fields we demonstrate a strong (88% on-off contrast) laser induced\nswitching of the optical response. The results represent an electrically\ntunable, discrete coupled quantum system with a conditional optical response.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Fano resonance in Raman scattering of graphene: Fano resonances and their strong doping dependence are observed in Raman\nscattering of single-layer graphene (SLG). As the Fermi level is varied by a\nback-gate bias, the Raman G band of SLG exhibits an asymmetric line shape near\nthe charge neutrality point as a manifestation of a Fano resonance, whereas the\nline shape is symmetric when the graphene sample is electron or hole doped.\nHowever, the G band of bilayer graphene (BLG) does not exhibit any Fano\nresonance regardless of doping. The observed Fano resonance can be interpreted\nas interferences between the phonon and excitonic many-body spectra in SLG. The\nabsence of a Fano resonance in the Raman G band of BLG can be explained in the\nsame framework since excitonic interactions are not expected in BLG.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron transport in semiconducting carbon nanotubes with\n  hetero-metallic contacts: We present an atomistic self-consistent study of the electronic and transport\nproperties of semiconducting carbon nanotube in contact with metal electrodes\nof different work functions, which shows simultaneous electron and hole doping\ninside the nanotube junction through contact-induced charge transfer. We find\nthat the band lineup in the nanotube bulk region is determined by the effective\nwork function difference between the nanotube channel and source/drain\nelectrodes, while electron transmission through the SWNT junction is affected\nby the local band structure modulation at the two metal-nanotube interfaces,\nleading to an effective decoupling of interface and bulk effects in electron\ntransport through nanotube junction devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Using nonlocal surface transport to identify the axion insulator: The axion is a hypothetical but experimentally undetected particle. Recently,\nthe antiferromagnetic topological insulator MnBi$_2$Te$_4$ has been predicted\nto host the axion insulator, but the experimental evidence remains elusive.\nSpecifically, the axion insulator is believed to carry \"half-quantized\" chiral\ncurrents running antiparallel on its top and bottom surfaces. However, it is\nchallenging to measure precisely the half-quantization. Here, we propose a\nnonlocal surface transport device, in which the axion insulator can be\ndistinguished from normal insulators without a precise measurement of the\nhalf-quantization. More importantly, we show that the nonlocal surface\ntransport, as a qualitative measurement, is robust in realistic situations when\nthe gapless side surfaces and disorder come to play. Moreover, thick electrodes\ncan be used in the device of MnBi$_2$Te$_4$ thick films, enhancing the\nfeasibility of the surface measurements. This proposal will be insightful for\nthe search of the axion insulator and axion in topological matter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Confinement in Si and Ge Nanostructures: We apply perturbative effective mass theory as a broadly applicable\ntheoretical model for quantum confinement (QC) in all Si and Ge nanostructures\nincluding quantum wells (QWs), wires (Q-wires) and dots (QDs). Within the\nlimits of strong, medium, and weak QC, valence and conduction band edge energy\nlevels (VBM and CBM) were calculated as a function of QD diameters, QW\nthicknesses and Q-wire diameters. Crystalline and amorphous quantum systems\nwere considered separately. Calculated band edge levels with strong, medium and\nweak QC models were compared with experimental VBM and CBM reported from X-ray\nphotoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS) or\nphotoluminescence (PL). Experimentally, the dimensions of the nanostructures\nwere determined directly, by transmission electron microscopy (TEM), or\nindirectly, by x-ray diffraction (XRD) or by XPS. We found that crystalline\nmaterials are best described by a medium confinement model, while amorphous\nmaterials exhibit strong confinement regardless of the dimensionality of the\nsystem. Our results indicate that spatial delocalization of the hole in\namorphous versus crystalline nanostructures is the important parameter\ndetermining the magnitude of the band gap expansion, or the strength of the\nquantum confinement. In addition, the effective masses of the electron and hole\nare discussed as a function of crystallinity and spatial confinement.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dark Exciton Giant Rabi Oscillations with no External Magnetic Field: Multi-phonon physics is an emerging field that serves as a test bed for\nfundamental quantum physics and several applications in metrology, on-chip\ncommunication, among others. Quantum acoustic cavities or resonators are\ndevices that are being used to study multi-phonon phenomena both theoretically\nand experimentally. In particular, we study a system consisting of a\nsemiconductor quantum dot pumped by a driving laser, and coupled to an acoustic\ncavity. This kind of systems has proven to yield interesting multi-phonon\nphenomena, but the description of the quantum dot has been limited to a\ntwo-level system. This limitation restrains the complexity that a true\nsemiconductor quantum dot can offer. Instead, in this work we consider a model\nwhere the quantum dot can have both bright and dark excitons, the latter being\nparticularly useful due to their lower decoherence rates, because they do not\npresent spontaneous photon emission. In this setup, we demonstrate that by\nfine-tuning the driving laser frequency, one is able to realise giant Rabi\noscillations between the vacuum state and a dark exciton state with $N$-phonon\nbundles. From this, we highlight two outstanding features: first, we are able\nto create dark states excitations in the quantum dot without the usual external\nmagnetic field needed to do so; and second, in a dissipative scenario where the\nacoustic cavity and the quantum dot suffer from losses, the system acts as a\nphonon gun able to emit $N$-phonon bundles.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Linear-response magnetoresistance effects in chiral systems: The chirality-induced spin selectivity (CISS) effect enables the detection of\nchirality as electrical charge signals. It is often studied using a\ntwo-terminal circuit geometry where a ferromagnet is connected to a chiral\ncomponent, and a change of electrical resistance is reported upon magnetization\nreversal. This is however not expected in the linear response regime because of\ncompensating reciprocal processes, limiting the interpretation of experimental\nresults. Here we show that magnetoresistance effects can indeed appear even in\nthe linear response regime, either by changing the magnitude or the direction\nof the magnetization or an applied magnetic field. We illustrate this in a\nspin-valve device and in a chiral thin film as the CISS-induced Hanle\nmagnetoresistance (CHMR) effect. This effect helps to distinguish\nspin-transport-related effects from other effects, and can thereby provide\nfurther insight into the origin of CISS.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Band geometry from position-momentum duality at topological band\n  crossings: We show that the position-momentum duality offers a transparent\ninterpretation of the band geometry at the topological band crossings. Under\nthis duality, the band geometry with Berry connection is dual to the\nfree-electron motion under gauge field. This identifies the trace of quantum\nmetric as the dual energy in momentum space. The band crossings with Berry\ndefects thus induce the dual energy quantization in the trace of quantum\nmetric. For the $\\mathbb Z$ nodal-point and nodal-surface semimetals in three\ndimensions, the dual Landau level quantization occurs owing to the Berry\ncharges. Meanwhile, the two-dimensional (2D) Dirac points exhibit the Berry\nvortices, leading to the quantized dual axial rotational energies. Such a\nquantization naturally generalizes to the three-dimensional (3D) nodal-loop\nsemimetals, where the nodal loops host the Berry vortex lines. The $\\mathbb\nZ_2$ monopoles bring about additional dual axial rotational energies, which\noriginate from the links with additional nodal lines. Nontrivial band geometry\ngenerically induces finite spread in the Wannier functions. While the spread\nmanifest quantized lower bounds from the Berry charges, logarithmic divergences\noccur from the Berry vortices. The band geometry at the band crossings may be\nprobed experimentally by a periodic-drive measurement.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Coherent tunnelling across a quantum point contact in the quantum Hall\n  regime: The unique properties of quantum Hall devices arise from the ideal\none-dimensional edge states that form in a two-dimensional electron system at\nhigh magnetic field. Tunnelling between edge states across a quantum point\ncontact (QPC) has already revealed rich physics, like fractionally charged\nexcitations, or chiral Luttinger liquid. Thanks to scanning gate microscopy, we\nshow that a single QPC can turn into an interferometer for specific potential\nlandscapes. Spectroscopy, magnetic field and temperature dependences of\nelectron transport reveal a quantitatively consistent interferometric behavior\nof the studied QPC. To explain this unexpected behavior, we put forward a new\nmodel which relies on the presence of a quantum Hall island at the centre of\nthe constriction as well as on different tunnelling paths surrounding the\nisland, thereby creating a new type of interferometer. This work sets the\nground for new device concepts based on coherent tunnelling.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electrical Transport Across an Individual Magnetic Domain Wall in\n  (Ga,Mn)As Microdevices: Recent studies demonstrate that an individual magnetic domain wall (DW) can\nbe trapped and reproducibly positioned within multiterminal (Ga,Mn)As\nmicrodevices. The electrical resistance obtained from such measurements is\nfound to be measurably altered by the presence of this single entity. To\nelucidate these observations we develop a simple model for the electrical\npotential distribution along a multiterminal device in the presence of a single\nDW. This is employed to calculate the effect of a single DW upon the\nlongitudinal and transverse resistance. The model provides very good agreement\nwith experimental observations, and serves to highlight important deviations\nfrom simple theory. We show that measurements of transverse resistance along\nthe channel permits establishing the position and the shape of the DW contained\nwithin it. An experimental scheme is developed that enables unambiguous\nextraction of the intrinsic DW resistivity. This permits the intrinsic\ncontribution to be differentiated from resistivities originating from the bulk\nand from magnetic anisotropy - effects that are generally manifested as large\nbackgrounds in the experiments.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "2D MoS2-Graphene-based multilayer van der Waals heterostructures:\n  Enhanced charge transfer and optical absorption, and electric-field tunable\n  Dirac point and band gap: Multilayer van der Waals (vdWs) heterostructures assembled by diverse\natomically thin layers have demonstrated a wide range of fascinating phenomena\nand novel applications. Understanding the interlayer coupling and its\ncorrelation effect is paramount for designing novel vdWs heterostructures with\ndesirable physical properties. Using a detailed theoretical study of 2D\nMoS2-graphene (GR)-based heterostructures based on state-of-the-art hybrid\ndensity functional theory, we reveal that for 2D few-layer heterostructures,\nvdWs forces between neighboring layers depend on the number of layers. Compared\nto that in bilayer, the interlayer coupling in trilayer vdW heterostructures\ncan significantly be enhanced by stacking the third layer, directly supported\nby short interlayer separations and more interfacial charge transfer. The\ntrilayer shows strong light absorption over a wide range (<700 nm), making it\nvery potential for solar energy harvesting and conversion. Moreover, the Dirac\npoint of GR and band gaps of each layer and trilayer can be readily tuned by\nexternal electric field, verifying multilayer vdWs heterostructures with unqiue\noptoelectronic properties found by experiments. These results suggest that\ntuning the vdWs interaction, as a new design parameter, would be an effective\nstrategy for devising particular 2D multilayer vdWs heterostructures to meet\nthe demands in various applications.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Positive longitudinal spin magnetoconductivity in $\\mathbb{Z}_{2}$\n  topological Dirac semimetals: Recently, a class of Dirac semimetals, such as \\textrm{Na}$_{\\mathrm{3}}%\n$\\textrm{Bi} and \\textrm{Cd}$_{\\mathrm{2}}$\\textrm{As}$_{\\mathrm{3}}$, are\ndiscovered to carry $\\mathbb{Z}_{2}$ monopole charges. We present an\nexperimental mechanism to realize the $\\mathbb{Z}_{2}$ anomaly in regard to the\n$\\mathbb{Z}_{2}$ topological charges, and propose to probe it by\nmagnetotransport measurement. In analogy to the chiral anomaly in a Weyl\nsemimetal, the acceleration of electrons by a spin bias along the magnetic\nfield can create a $\\mathbb{Z}_{2}$ charge imbalance between the Dirac points,\nthe relaxation of which contributes a measurable positive longitudinal spin\nmagnetoconductivity (LSMC) to the system. The $\\mathbb{Z}_{2}$ anomaly induced\nLSMC is a spin version of the longitudinal magnetoconductivity (LMC) due to the\nchiral anomaly, which possesses all characters of the chiral anomaly induced\nLMC. While the chiral anomaly in the topological Dirac semimetal is very\nsensitive to local magnetic impurities, the $\\mathbb{Z}_{2}$ anomaly is found\nto be immune to local magnetic disorder. It is further demonstrated that the\nquadratic or linear field dependence of the positive LMC is not unique to the\nchiral anomaly. Base on this, we argue that the periodic-in-$1/B$ quantum\noscillations superposed on the positive LSMC can serve as a fingerprint of the\n$\\mathbb{Z}_{2}$ anomaly in topological Dirac semimetals.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Andreev-Coulomb Drag in Coupled Quantum Dots: The Coulomb drag effect has been observed as a tiny current induced by both\nelectron-hole asymmetry and interactions in normal coupled quantum dot devices.\nIn the present work we show that the effect can be boosted by replacing one of\nthe normal electrodes by a superconducting one. Moreover, we show that at low\ntemperatures and for sufficiently strong coupling to the superconducting lead,\nthe Coulomb drag is dominated by Andreev processes, is robust against details\nof the system parameters and can be controlled with a single gate voltage. This\nmechanism can be distinguished from single-particle contributions by a sign\ninversion of the drag current.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Effects of mechanical rotation on spin currents: We study the Pauli--Schr\\\"odinger equation in a uniformly rotating frame of\nreference to describe a coupling of spins and mechanical rotations. The\nexplicit form of the spin-orbit interaction (SOI) with the inertial effects due\nto the mechanical rotation is presented. We derive equations of motion for a\nwavepacket of electrons in two-dimensional planes subject to the SOI. The\nsolution is a superposition of two cyclotron motions with different frequencies\nand a circular spin current is created by the mechanical rotation.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunable terahertz radiation from graphene induced by moving electrons: Based on a structure consisting of a single graphene layer situated on a\nperiodic dielectric grating, we show theoretically that intense terahertz (THz)\nradiations can be generated by an electron bunch moving atop the graphene\nlayer. The underlying physics lies in the fact that a moving electron bunch\nwith rather low electron energy ($\\sim$1 keV) can efficiently excite graphene\nplasmons (GPs) of THz frequencies with a strong confinement of near-fields. GPs\ncan be further scattered into free space by the grating for those satisfying\nthe phase matching condition. The radiation patterns can be controlled by\nvarying the velocity of the moving electrons. Importantly, the radiation\nfrequencies can be tuned by varying the Fermi level of the graphene layer,\noffering tunable THz radiations that can cover a wide frequency range. Our\nresults could pave the way toward developing tunable and miniature THz\nradiation sources based on graphene.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Metamorphosis of Andreev bound states into Majorana bound states in\n  pristine nanowires: We show theoretically that in the generic finite chemical potential\nsituation, the clean superconducting spin-orbit-coupled nanowire has two\ndistinct nontopological regimes as a function of Zeeman splitting (below the\ntopological quantum phase transition): one is characterized by finite-energy\nin-gap Andreev bound states, while the other has only extended bulk states. The\nAndreev bound state regime is characterized by strong features in the tunneling\nspectra creating a \"gap closure\" signature, but no \"gap reopening\" signature\nshould be apparent above the topological quantum phase transition, in agreement\nwith most recent experimental observations. The gap closure feature is actually\nthe coming together of the Andreev bound states at high chemical potential\nrather than a simple trivial gap of extended bulk states closing at the\ntransition. Our theoretical finding establishes the generic intrinsic Andreev\nbound states on the trivial side of the topological quantum phase transition as\nthe main contributors to the tunneling conductance spectra, providing a generic\ninterpretation of existing experiments in clean Majorana nanowires. Our work\nalso explains why experimental tunnel conductance spectra generically have gap\nclosing features below the topological quantum phase transition, but no gap\nopening features above it.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Cyclotron resonance of single valley Dirac fermions in gapless HgTe\n  quantum well: We report on Landau level spectroscopy studies of two HgTe quantum wells\n(QWs) near or at the critical well thickness, where the band gap vanishes. In\nmagnetic fields up to $B$=16T, oriented perpendicular to the QW plane, we\nobserve a $\\sqrt{B}$ dependence for the energy of the dominant cyclotron\nresonance (CR) transition characteristic of two-dimensional Dirac fermions. The\ndominant CR line exhibits either a single or double absorption lineshape for\nthe gapless or gapped QW. Using an effective Dirac model, we deduce the band\nvelocity of single valley Dirac fermions in gapless HgTe quantum wells,\n$v_F=6.4 \\times10^5$ m/s, and interpret the double absorption of the gapped QW\nas resulting from the addition of a small relativistic mass.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum anomalies in nodal line semimetals: Topological semimetals is a new class of condensed matter systems with\nnontrivial electronic structure topology. Their unusual observable properties\nmay often be understood in terms of quantum anomalies. In particular, Weyl and\nDirac semimetals, which have point band touching nodes, are characterized by\nthe chiral anomaly, which leads to the Fermi arc surface states, anomalous Hall\neffect, negative longitudinal magnetoresistance and planar Hall effect. In this\npaper we explore analogous phenomena in nodal line semimetals. We demonstrate\nthat such semimetals realize a three dimensional analog of the parity anomaly,\nwhich is a known property of two dimensional Dirac semimetals arising, for\nexample, on the surface of a three dimensional topological insulator. We relate\none of the characteristic properties of nodal line semimetals, namely the\ndrumhead surface states, to this anomaly, and derive the field theory, which\nencodes the corresponding anomalous response.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Magnetotransport properties of granular oxide-segregated CoPtCr films\n  for applications in future magnetic memory technology: Magnetotransport properties of granular oxide-segregated CoPtCr films were\nstudied on both macroscopic and microscopic length scales by performing bulk\nand point-contact magnetoresistance measurements, respectively. Such a\nperpendicular magnetic medium is used in state-of-the-art hard disc drives and\nif combined with magnetoresistive phenomena (for read/write operations) may\nlead to a novel concept for magnetic recording with high areal density. While\nthe bulk measurements on the films showed only small variations in dc\nresistance as a function of applied magnetic field (magnetoresistance of less\nthan 0.02 %), the point-contact measurements revealed\ngiant-magnetoresistance-like changes in resistance with up to 50,000 % ratios.\nThe observed magnetorestive effect could be attributed to a tunnel\nmagnetoresistance between CoPtCr grains with different coercivity. The\ntunneling picture of electronic transport in our granular medium was confirmed\nby the observation of tunneling-like current-voltage characteristics and bias\ndependence of magnetoresistance; both the point-contact resistance and\nmagnetoresistance were found to decrease with the applied dc bias.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Generating surface states in a Weyl semi-metal by applying\n  electromagnetic radiation: We show that the application of circularly polarized electromagnetic\nradiation on the surface of a Weyl semi-metal can generate states at that\nsurface. These states can be characterized by their surface momentum. The\nFloquet eigenvalues of these states come in complex conjugate pairs rather than\nbeing equal to $\\pm 1$. If the amplitude of the radiation is small, we find\nsome unusual bulk-boundary relations: the Floquet eigenvalues of the surface\nstates lie at the extrema of the Floquet eigenvalues of the bulk system, and\nthe peaks of the Fourier transforms of the surface state wave functions lie at\nthe momenta where the bulk Floquet eigenvalues have extrema. For the case of\nzero surface momentum, we can analytically derive scaling relations between the\ndecay length of the surface states and the amplitude and penetration length of\nthe radiation. For topological insulators, we again find that circularly\npolarized radiation can generate states on the surfaces; these states have much\nlarger decay lengths than the surface states which are present even in the\nabsence of radiation. Finally, we show that radiation can generate surface\nstates for trivial insulators also.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Extending the spin excitation lifetime of a magnetic molecule on a\n  proximitized superconductor: Magnetic molecules deposited on surfaces are a promising platform to\nindividually address and manipulate spins. Long spin excitation lifetimes are\nnecessary to utilize them in quantum information processing and data storage.\nNormally, coupling of the molecular spin with the conduction electrons of\nmetallic surfaces causes fast relaxation of spin excitations into the ground\nstate. However, the presence of superconducting paring effects in the substrate\ncan protect the excited spin from decaying. In this work, we show that a\nproximity-induced superconducting gold film can sustain spin excitations of a\nFeTPP-Cl molecule for more than 80ns. This long value was determined by\nstudying inelastic spin excitations of the S=5/2 multiplet of FeTPP-Cl on Au\nfilms over V(100) using scanning tunneling spectroscopy. The spin lifetime\ndecreases with increasing film thickness, in apparent connection with the\ngradual gap-closing of a pair of de Gennes-Saint James resonances found inside\nthe superconducting gap. Our results elucidate the use of proximitized gold\nelectrodes for addressing quantum spins on surfaces, envisioning new routes for\ntuning the value of their spin lifetime.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Valley-selective exciton bistability in a suspended monolayer\n  semiconductor: We demonstrate robust power- and wavelength-dependent optical bistability in\nfully suspended monolayers of WSe2 near the exciton resonance. Bistability has\nbeen achieved under continuous-wave optical excitation at an intensity level of\n10^3 W/cm^2. The observed bistability is originated from a photo-thermal\nmechanism, which provides both optical nonlinearity and passive feedback, two\nessential elements for optical bistability. Under a finite magnetic field, the\nexciton bistability becomes helicity dependent, which enables repeatable\nswitching of light purely by its polarization.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Overlapping Andreev states in semiconducting nanowires: competition of\n  1D and 3D propagation: The recent proposals of devices with overlapping Andreev bound states (ABS)\nopen up the opportunities to control and fine-tune their spectrum, that can be\nused in various applications. In this Article, we study the ABS in a device\nconsisting of a semiconducting nanowire covered with three superconducting\nleads. The ABS are formed at two junctions where the wire is not covered. They\noverlap in the wire where the electron propagation is 1D, and in one of the\nleads where the propagation is 3D. We identify a number of regimes where these\ntwo overlaps either dominate or compete, depending on the junction separation\n$L$ as compared to the correlation lengths $\\xi_{\\rm w}$, $\\xi_{\\rm s}$ in the\nwire and in the lead, respectively. We utilize a simple model of 1D electron\nspectrum in the nanowire and take into account the quality of the contact\nbetween the nanowire and the superconducting lead. We present the spectra for\ndifferent $L$, detailing the transition from a single-ABS in the regime of\nstrong 1D hybridization to two almost independent ABS hybridized at the\ndegeneracy points, in the regime of weak 1D hybridization. We present the\ndetails of merging the upper ABS with the continuous spectrum upon decreasing\n$L$. We study in detail the effect of quantum interference due to the phase\naccumulated during the electron passage between the junctions. We develop a\nperturbation theory for analytical treatment of hybridization. We address an\ninteresting separate case of fully transparent junctions. We derive and\nexemplify a perturbation theory suitable for the competition regime\ndemonstrating the interference of 1D and two 3D transmission amplitudes.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anomalous Thermal Transport in Quantum Wires: We study thermal transport in a one-dimensional quantum wire, connected to\nreservoirs. Despite of the absence of electron backscattering, interactions in\nthe wire strongly influence thermal transport. Electrons propagate with unitary\ntransmission through the wire and electric conductance is not affected. Energy,\nhowever, is carried by bosonic excitations (plasmons) which suffer from\nscattering even on scales much larger than the Fermi wavelength. If the\nelectron density varies randomly, plasmons are localized and {\\em charge-energy\nseparation} occurs. We also discuss the effect of plasmon-plasmon interaction\nusing Levinson's theory of nonlocal heat transport.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Transport through quantum spin Hall insulator/metal junctions in\n  graphene ribbons: Quantum spin Hall insulator/metal interfaces are formed in graphene ribbons\nwith intrinsic spin-orbit coupling by selectively doping two regions creating a\npotential step. For a clean graphene ribbon, the transmission of the\ntopological edge states through a n-n or p-p junction is perfect irrespective\nof the ribbon termination, width, and potential step parameters due to the\northogonality of incoming and outgoing edge channels. This is shown numerically\nfor an arbitrary crystallographic orientation of the ribbon and proven\nanalytically for zigzag and metallic armchair boundary conditions. In\ndisordered ribbons, the orthogonality between left- and right-movers is in\ngeneral destroyed and backscattering sets in. However, transmission approaches\none by increasing the ribbon's width, even in the presence of strong edge\nroughness.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Switching 2D Magnetic States via Pressure Tuning of Layer Stacking: The physical properties of two-dimensional van der Waals (2D vdW) crystals\ndepend sensitively on the interlayer coupling, which is intimately connected to\nthe stacking arrangement and the interlayer spacing. For example, simply\nchanging the twist angle between graphene layers can induce a variety of\ncorrelated electronic phases, which can be controlled further in a continuous\nmanner by applying hydrostatic pressure to decrease the interlayer spacing. In\nthe recently discovered 2D magnets, theory suggests that the interlayer\nexchange coupling strongly depends on layer separation, while the stacking\narrangement can even change the sign of the magnetic exchange, thus drastically\nmodifying the ground state. Here, we demonstrate pressure tuning of magnetic\norder in the 2D magnet CrI3. We probe the magnetic states using tunneling and\nscanning magnetic circular dichroism microscopy measurements. We find that the\ninterlayer magnetic coupling can be more than doubled by hydrostatic pressure.\nIn bilayer CrI3, pressure induces a transition from layered antiferromagnetic\nto ferromagnetic phases. In trilayer CrI3, pressure can create coexisting\ndomains of three phases, one ferromagnetic and two distinct antiferromagnetic.\nThe observed changes in magnetic order can be explained by changes in the\nstacking arrangement. Such coupling between stacking order and magnetism\nprovides ample opportunities for designer magnetic phases and functionalities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Tunable strong coupling of mechanical resonance between spatially\n  separated FePS$_3$ nanodrums: Coupled nanomechanical resonators made of two-dimensional materials are\npromising for processing information with mechanical modes. However, the\nchallenge for these types of systems is to control the coupling. Here, we\ndemonstrate strong coupling of motion between two suspended membranes of the\nmagnetic 2D material FePS$_3$. We describe a tunable electromechanical\nmechanism for control over both the resonance frequency and the coupling\nstrength using a gate voltage electrode under each membrane. We show that the\ncoupling can be utilized for transferring data from one drum to the other by\namplitude modulation. Finally, we also study the temperature dependence of the\ncoupling, and in particular how it is affected by the antiferromagnetic phase\ntransition characteristic of this material. The presented electrical coupling\nof resonant magnetic 2D membranes holds promise of transferring mechanical\nenergy over a distance at low electrical power, thus enabling novel data\nreadout and information processing technologies.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Polarization bistability and resultant spin rings in semiconductor\n  microcavities: The transmission of a pump laser resonant with the lower polariton branch of\na semiconductor microcavity is shown to be highly dependent on the degree of\ncircular polarization of the pump. Spin dependent anisotropy of\npolariton-polariton interactions allows the internal polarization to be\ncontrolled by varying the pump power. The formation of spatial patterns, spin\nrings with high degree of circular polarization, arising as a result of\npolarization bistability, is observed. A phenomenological model based on spin\ndependent Gross-Pitaevskii equations provides a good description of the\nexperimental results. Inclusion of interactions with the incoherent exciton\nreservoir, which provides spin-independent blueshifts of the polariton modes,\nis found to be essential.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Moderate bandgap and high carrier mobility simultaneously realized in\n  bilayer silicene by oxidation: Semiconductors simultaneously possessing high carrier mobility, moderate\nbandgap, and ambient environment stability are so important for the modern\nindustry, and Si-based semiconducting materials can match well with the\nprevious silicon based electronic components. Thus, searching for such Si-based\nsemiconductors has been one hot project due to the lack of them nowadays. Here,\nwith the help of density functional theory, we found that the oxidized bilayer\nsilicene exhibits high carrier mobility with a moderate direct bandgap of 1.02\neV. The high carrier mobility is caused by the remaining of big pi bond, and\nthe moderate bandgap is opened by the saturation of dangling Si 3p bonds.\nOriginated from the formation of strong Si-O and Si-Si bonds, the sample\nexhibits strong thermodynamic and dynamical stabilities. Our work indicates\nthat the oxidized bilayer silicene has many potential applications in modern\nelectronic fields.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Full Counting Statistics of a Non-adiabatic Electron Pump: Non-adiabatic charge pumping through a single-level quantum dot with\nperiodically modulated parameters is studied theoretically. By means of a\nquantum-master-equation approach the full counting statistics of the system is\nobtained. We find a trinomial-probability distribution of the charge transfer,\nwhich adequately describes the reversal of the pumping current by sweeping the\ndriving frequency. Further, we derive equations of motion for current and\nnoise, and solve those numerically for two different driving schemes. Both show\ninteresting features which can be fully analyzed due to the simple and generic\nmodel studied.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Step-like features on caloric effects of graphenes: We considered a graphene nano-ribbon with a longitudinal electric field\n(along $x$ direction) and a transversal magnetic field (along $z$ direction),\nand then observe (i) the electrocaloric effect ruled by an applied magnetic\nfield and (ii) the magnetocaloric effect ruled by an applied electric field. We\nfocused our attention to the limit of low temperatures, and then observed\ninteresting step-like features. For each filled Landau level $n$, created by\nthe applied magnetic field, both caloric effects increase proportionally to\n$n+1/2$; and this step measures either important graphene properties (like\nFermi velocity) or quantum fundamental quantities (like Planck constant and\nmagnetic flux quantum).",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Size-dependent spatial magnetization profile of manganese-zinc ferrite\n  Mn0.2Zn0.2Fe2.6O4 nanoparticles: We report the results of an unpolarized small-angle neutron scattering (SANS)\nstudy on Mn-Zn ferrite (MZFO) magnetic nanoparticles with the aim to elucidate\nthe interplay between their particle size and the magnetization configuration.\nWe study different samples of single-crystalline MZFO nanoparticles with\naverage diameters ranging between 8 to 80 nm, and demonstrate that the smallest\nparticles are homogeneously magnetized. However, with increasing nanoparticle\nsize, we observe the transition from a uniform to a nonuniform magnetization\nstate. Field-dependent results for the correlation function confirm that the\ninternal spin disorder is suppressed with increasing field strength. The\nexperimental SANS data are supported by the results of micromagnetic\nsimulations, which confirm an increasing inhomogeneity of the magnetization\nprofile of the nanoparticle with increasing size. The results presented\ndemonstrate the unique ability of SANS to detect even very small deviations of\nthe magnetization state from the homogeneous one.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Near-field infrared nano-spectroscopy of surface phonon-polariton\n  resonances: We present combined experimental and numerical work on light-matter\ninteractions at nanometer length scales. We report novel numerical simulations\nof near-field infrared nanospectroscopy that consider, for the first time,\ndetailed tip geometry and have no free parameters. Our results match published\nspectral shapes of amplitude and phase measurements even for strongly resonant\nsurface phonon-polariton (SPhP) modes. They also verify published absolute\nscattering amplitudes for the first time. A novel, ultrabroadband light source\nenables near-field amplitude and phase acquisition into the far-infrared\nspectral range. This allowed us to discover a strong SPhP resonance in the\npolar dielectric SrTiO3 (STO) at approximately 24 micrometer wavelength of\nincident light.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Instanton Approach to Josephson Tunneling between Trapped Condensates: An instanton method is proposed to investigate the quantum tunneling between\ntwo weakly-linked Bose-Einstein condensates confined in double-well potential\ntraps. We point out some intrinsic pathologies in the earlier treatments of\nother authors and make an effort to go beyond these very simple zero order\nmodels. The tunneling amplitude may be calculated in the Thomas-Fermi\napproximation and beyond it; we find it depends on the number of the trapped\natoms, through the chemical potential. Some suggestions are given for the\nobservation of the Josephson oscillation and the MQST.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Universal dephasing in a chiral 1D interacting fermion system: We consider dephasing by interactions in a one-dimensional chiral fermion\nsystem (e.g. a Quantum Hall edge state). For finite-range interactions, we\ncalculate the spatial decay of the Green's function at fixed energy, which sets\nthe contrast in a Mach-Zehnder interferometer. Using a physically transparent\nsemiclassical ansatz, we find a power-law decay of the coherence at high\nenergies and zero temperature (T=0), with a universal asymptotic exponent of 1,\nindependent of the interaction strength. We obtain the dephasing rate at T>0\nand the fluctuation spectrum acting on an electron.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Acoustic plasmons in graphene sandwiched between two metallic slabs: We study the effect of two metallic slabs on the collective dynamics of\nelectrons in graphene positioned between the two slabs. We show that if the\nslabs are perfect conductors the plasmons of graphene display a linear\ndispersion relation. The velocity of these acoustic plasmons crucially depends\non the distance between the two metal gates and the graphene sheet. In the case\nof generic slabs, the dispersion relation of graphene plasmons is much more\ncomplicated but we find that acoustic plasmons can still be obtained under\nspecific conditions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Flat bands and chiral optical response of moir\u00e9 insulators: We present a low-energy model describing the reconstruction of the electronic\nspectrum in twisted bilayers of honeycomb crystals with broken sublattice\nsymmetry. The resulting moir\\'e patterns are classified into two families with\ndifferent symmetry. In both cases, flat bands appear at relatively large\nangles, without any magic angle condition. Transitions between them give rise\nto sharp resonances in the optical absorption spectrum at frequencies well\nbelow the gap of the monolayer. Owing to their chiral symmetry, twisted\nbilayers display circular dichroism, i.e., different absorption of left and\nright circularly-polarized light. This optical activity is a nonlocal property\ndetermined by the stacking. In hexagonal boron nitride, sensitivity to the\nstacking leads to strikingly different circular dichroism in the two types of\nmoir\\'es. Our calculations exemplify how subtle properties of the electronic\nwavefunctions encoded in current correlations between the layers control\nphysical observables of moir\\'e materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Field-effect tunneling transistor based on vertical graphene\n  heterostructures: We report a bipolar field effect tunneling transistor that exploits to\nadvantage the low density of states in graphene and its one atomic layer\nthickness. Our proof-of-concept devices are graphene heterostructures with\natomically thin boron nitride acting as a tunnel barrier. They exhibit room\ntemperature switching ratios ~50, a value that can be enhanced further by\noptimizing the device structure. These devices have potential for high\nfrequency operation and large scale integration.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Interference of diffusing photons and level crossing spectroscopy: We show that a new interference effect appears in the intensity fluctuations\nof photons multiply scattered by an atomic gas of large optical depth b. This\ninterference occurs only for scattering atoms that are Zeeman degenerate and it\nleads to a deviation from the Rayleigh law. The fluctuations measured by their\nvariance, display a resonance peak as a function of an applied magnetic field.\nThe resonance width is proportional to the small factor 1/b. We derive closed\nanalytic expressions for all these physical quantities which are directly\naccessible experimentally.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Disorder-mediated Kondo effect in graphene: We study the emergence of strongly correlated states and Kondo physics in\ndisordered graphene. Diluted short range disorder gives rise to localized\nmidgap states at the vicinity of the system charge neutrality point. We show\nthat long-range disorder, ubiquitous in graphene, allows for the coupling of\nthese localized states to an effective (disorder averaged) metallic band. The\nsystem is described by an Anderson-like model. We use the numerical\nrenormalization group (NRG) method to study the distributions of Kondo\ntemperatures $P(T_K)$. The results show that disorder can lead to long\nlogarithmic tails in $P(T_K)$, consistent with a quantum Griffiths phase.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Giant excitonic magneto-optical Faraday rotation in single semimagnetic\n  CdTe/Cd_{1-x}Mn_{x}Te quantum ring: Magnetic tuning of the bound exciton states and corresponding giant Zeeman\nsplitting (GZS) between {\\sigma}^{+} and {\\sigma}^{-} excitonic transitions in\nCdTe/Cd_{1-x}Mn_{x}Te quantum ring has been investigated in the Faraday\nconfiguration for various concentrations of Mn^{2+} ions, using the variational\ntechnique in the effective mass approximation. The sp-d exchange interaction\nbetween the localized magnetic impurity ions and the delocalized charge\ncarriers has been accounted via mean-field theory with the inclusion of a\nmodified Brillouin function. The enhancement of the GZS, and in turn, the\neffective g-factor with the application of an external magnetic field, is\nstrikingly manifested in type-I - type-II transition in the band structure,\nwhich has been well explained by computing the overlap integral between the\nelectron and hole, and the in-plane exciton radius. This highlights the\nextraordinary magneto-optical properties, including the giant Faraday rotation\nand associated Verdet constant, which have been calculated using single\noscillator model. The oscillator strength and exciton lifetime have been\nestimated, and are found to be larger than in the bulk diluted magnetic\nsemiconductors (DMS) and quantum wells, reflecting stronger confinement inside\nthe quantum ring. The results show that the DMS-based quantum ring exhibits\nmore extensive Zeeman splitting, which gives rise to ultra-high Verdet constant\nof 2.6 \\times 10^{9}rad/Tesla/m, which are a few orders of magnitude larger\nthan in the existing quantum systems and magneto-optical materials.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Topological qubits in graphenelike systems: The fermion-doubling problem can be an obstacle to getting half-a-qubit in\ntwo-dimensional fermionic tight-binding models in the form of Majorana zero\nmodes bound to the core of superconducting vortices. We argue that the number\nof such Majorana zero modes is determined by a Z_2 x Z_2 topological charge for\na family of two-dimensional fermionic tight-binding models ranging from\nnoncentrosymmetric materials to graphene. This charge depends on the dimension\nof the representation (i.e., the number of species of Dirac fermions -- where\nthe doubling problem enters) and the parity of the Chern number induced by\nbreaking time-reversal symmetry. We show that in graphene there are as many as\nten order parameters that can be used in groups of four to change the\ntopological number from even to odd.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Novel mechanisms to enhance the capacitance beyond the classical limits\n  in capacitors with free-electron-like electrodes: The so-called negative electron compressibility refers to the lowering of the\nchemical potential of a metallic system when the carrier density increases.\nThis effect has often been invoked in the past to explain the enhancement of\nthe capacitance beyond the classical limits in capacitors with two-dimensional\nelectron gases as electrodes. Based on experiments on strongly confined\nsemiconductor quantum wells (QWs), it has been traditionally ascribed to the\nelectron exchange energy as the main driving force. Recent research, however,\nhas revealed that analogous effects can occur in other classes of materials\nsystems, such as polar oxide interfaces, whose characteristics drastically\ndepart from those of the previously considered cases. To rationalize these new\nresults, it is necessary to revisit the established theory of confined electron\ngases, and test whether its conclusions are valid beyond the specifics of\nsemiconductor-based QWs. Here we find, based on first-principles calculations\nof jellium slabs, that one must indeed be very careful when extrapolating\nexisting results to other realistic physical systems. In particular, we\nidentify a number of additional, previously overlooked mechanisms (e.g.,\nrelated to the displacement of the electronic cloud and to the multiband\nstructure of the delocalized gas), that enter into play and become new sources\nof negative capacitance in the weak-confinement regime. Our detailed analysis\nof these emerging contributions, supported by analytic models and multiple test\ncases, will provide a useful guidance in the ongoing quest for nanometric\ncapacitors with enhanced performance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Valley degeneracy in biaxially strained aluminum arsenide quantum wells: This paper details a complete formalism for calculating electron subband\nenergy and degeneracy in strained multi-valley quantum wells grown along any\norientation with explicit results for the AlAs quantum well case. A\nstandardized rotation matrix is defined to transform from the conventional-\ncubic-cell basis to the quantum-well-transport basis whereby effective mass\ntensors, valley vectors, strain matrices, anisotropic strain ratios, and\nscattering vectors are all defined in their respective bases. The specific\ncases of (001)-, (110)-, and (111)-oriented aluminum arsenide (AlAs) quantum\nwells are examined, as is the unconventional (411) facet, which is of\nparticular importance in AlAs literature. Calculations of electron confinement\nand strain in the (001), (110), and (411) facets determine the critical well\nwidth for crossover from double- to single-valley degeneracy in each system.\nThe notation is generalized to include miscut angles, and can be adapted to\nother multi-valley systems. To help classify anisotropic inter-valley\nscattering events, a new primitive unit cell is defined in momentum space which\nallows one to distinguish purely in-plane inter-valley scattering events from\nthose that requires an out-of-plane momentum scattering component.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Kinetics of Exciton Emission Patterns and Carrier Transport: We report on the measurements of the kinetics of expanding and collapsing\nrings in the exciton emission pattern. The rings are found to preserve their\nintegrity during expansion and collapse, indicating that the observed kinetics\nis controlled by charge carrier transport rather than by a much faster process\nof exciton production and decay. The relation between ring kinetics and carrier\ntransport, revealed by our experiment and confirmed by comparison with a\ntheoretical model, is used to determine electron and hole transport\ncharacteristics in a contactless fashion.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Heat transport in harmonic lattices: We work out the non-equilibrium steady state properties of a harmonic lattice\nwhich is connected to heat reservoirs at different temperatures. The heat\nreservoirs are themselves modeled as harmonic systems. Our approach is to write\nquantum Langevin equations for the system and solve these to obtain steady\nstate properties such as currents and other second moments involving the\nposition and momentum operators. The resulting expressions will be seen to be\nsimilar in form to results obtained for electronic transport using the\nnon-equilibrium Green's function formalism. As an application of the formalism\nwe discuss heat conduction in a harmonic chain connected to self-consistent\nreservoirs. We obtain a temperature dependent thermal conductivity which, in\nthe high-temperature classical limit, reproduces the exact result on this model\nobtained recently by Bonetto, Lebowitz and Lukkarinen.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Scaling for rectification of bipolar nanopores as a function of a\n  modified Dukhin number: the case of 1:1 electrolytes: The scaling behavior for the rectification of bipolar nanopores is studied\nusing the Nernst-Planck equation coupled to the Local Equilibrium Monte Carlo\nmethod. The bipolar nanopore's wall carries $\\sigma$ and $-\\sigma$ surface\ncharge densities in its two half regions axially. Scaling means that the device\nfunction (rectification) depends on the system parameters (pore length, $H$,\npore radius, $R$, concentration, $c$, voltage, $U$, and surface charge density,\n$\\sigma$) via a single scaling parameter that is a smooth analytical function\nof the system parameters. Here, we suggest using a modified Dukhin number,\n$\\mathrm{mDu}=|\\sigma|l_{\\mathrm{B}}^{*}\\lambda_{\\mathrm{D}}HU/(RU_{0})$, where\n$l_{\\mathrm{B}}^{*}=8\\pi l_{\\mathrm{B}}$, $l_{\\mathrm{B}}$ is the Bjerrum\nlength, $\\lambda_{\\mathrm{D}}$ is the Debye length, and $U_{0}$ is a reference\nvoltage. We show how scaling depends on $H$, $U$, and $\\sigma$ and through what\nmechanisms these parameters influence the pore's behavior.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Scaling properties of induced density of chiral and non-chiral Dirac\n  fermions in magnetic fields: We find that a repulsive potential of graphene in the presence of a magnetic\nfield has bound states that are peaked inside the barrier with tails extending\nover \\ell(N + 1), where \\ell and N are the magnetic length and Landau level(LL)\nindex. We have investigated how these bound states affect scaling properties of\nthe induced density of filled Landau levels of massless Dirac fermions. For\nchiral fermions we find, in strong coupling regime, that the density inside the\nrepulsive potential can be greater than the value in the absence of the\npotential while in the weak coupling regime we find negative induced density.\nSimilar results hold also for non-chiral fermions. As one moves from weak to\nstrong coupling regimes the effective coupling constant between the potential\nand electrons becomes more repulsive, and then it changes sign and becomes\nattractive. Different power-laws of induced density are found for chiral and\nnon-chiral fermions.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Minimal model for charge transfer excitons at the dielectric interface: Theoretical description of the charge transfer (CT) exciton across the\ndonor-acceptor interface without the use of a completely localized hole (or\nelectron) is a challenge in the field of organic solar cells. We calculate the\ntotal wavefunction of the CT exciton by solving an effective two-particle\nSchrodinger equation for the inhomogeneous dielectric interface. We formulate\nthe magnitude of the CT and construct a minimal model of the CT exciton under\nthe breakdown of inversion symmetry. We demonstrate that both a light hole mass\nand a hole localization along the normal to the dielectric interface are\ncrucial to yield the CT exciton.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Robustness of the quantum Hall effect, sample size versus sample\n  topology, and quality control management of III-V molecular beam epitaxy: We measure the IQHE on macroscopic (1.5cm x 1.5cm) \"quick 'n' dirty\" prepared\nIII-V heterostructure samples with van der Pauw and modified Corbino geometries\nat 1.3 K. We compare our results with (i) data taken on smaller specimens,\namong them samples with a standard Hall bar geometry, (ii) results of our\nnumerical analysis taking inhomogenities of the 2DEG into account. Our main\nfinding is a confirmation of the expected robustness of the IQHE which favours\nthe development of wide plateaux for small filling factors and very large\nsample sizes (here with areas 10,000 times larger than in standard\narrangements).",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Realization of a Laughlin quasiparticle interferometer: Observation of\n  fractional statistics: In two dimensions, the laws of physics permit existence of anyons, particles\nwith fractional statistics which is neither Fermi nor Bose. That is, upon\nexchange of two such particles, the quantum state of a system acquires a phase\nwhich is neither 0 nor \\pi, but can be any value. The elementary excitations\n(Laughlin quasiparticles) of a fractional quantum Hall fluid have fractional\nelectric charge and are expected to obey fractional statistics. Here we report\nexperimental realization of a novel Laughlin quasiparticle interferometer,\nwhere quasiparticles of the 1/3 fluid execute a closed path around an island of\nthe 2/5 fluid and thus acquire statistical phase. Interference fringes are\nobserved as conductance oscillations as a function of magnetic flux, similar to\nthe Aharonov-Bohm effect. We observe the interference shift by one fringe upon\nintroduction of five magnetic flux quanta (5h/e) into the island. The\ncorresponding 2e charge period is confirmed directly in calibrated gate\nexperiments. These results constitute direct observation of fractional\nstatistics of Laughlin quasiparticles.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Double refraction and spin splitter in a normal-hexagonal semiconductor\n  junction: In analogy with light refraction at optical boundary, ballistic electrons\nalso undergo refraction when propagate across a semiconductor junction.\nEstablishing a negative refractive index in conventional optical materials is\ndifficult, but the realization of negative refraction in electronic system is\nconceptually straightforward, which has been verified in graphene p-n junctions\nin recent experiments. Here, we propose a model to realize double refraction\nand double focusing of electric current by a normal-hexagonal semiconductor\njunction. The double refraction can be either positive or negative, depending\non the junction being n-n type or p-n type. Based on the valley-dependent\nnegative refraction, a spin splitter (valley splitter) is designed at the p-n\njunction system, where the spin-up and spin-down electrons are focused at\ndifferent regions. These findings may be useful for the engineering of double\nlenses in electronic system and have underlying application of spin splitter in\nspintronics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Electron quantum dynamics in closed and open potentials at high magnetic\n  fields: Quantization and lifetime effects unified by semicoherent states: We have developed a Green's function formalism based on the use of an\novercomplete semicoherent basis of vortex states, specially devoted to the\nstudy of the Hamiltonian quantum dynamics of electrons at high magnetic fields\nand in an arbitrary potential landscape smooth on the scale of the magnetic\nlength. This formalism is used here to derive the exact Green's function for an\narbitrary quadratic potential in the special limit where Landau level mixing\nbecomes negligible. This solution remarkably embraces under a unified form the\ncases of confining and unconfining quadratic potentials. This property results\nfrom the fact that the overcomplete vortex representation provides a more\ngeneral type of spectral decomposition of the Hamiltonian operator than usually\nconsidered. Whereas confining potentials are naturally characterized by\nquantization effects, lifetime effects emerge instead in the case of\nsaddle-point potentials. Our derivation proves that the appearance of lifetimes\nhas for origin the instability of the dynamics due to quantum tunneling at\nsaddle points of the potential landscape. In fact, the overcompleteness of the\nvortex representation reveals an intrinsic microscopic irreversibility of the\nstates synonymous with a spontaneous breaking of the time symmetry exhibited by\nthe Hamiltonian dynamics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Generating quantizing pseudomagnetic fields by bending graphene ribbons: We analyze the mechanical deformations that are required to create uniform\npseudomagnetic fields in graphene. It is shown that, if a ribbon is bent\nin-plane into a circular arc, this can lead to fields exceeding 10T, which is\nsufficient for the observation of pseudo-Landau quantization. The arc geometry\nis simpler than those suggested previously and, in our opinion, has much better\nchances to be realized experimentally soon. The effects of a scalar potential\ninduced by dilatation in this geometry is shown to be negligible.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Dynamic frequency dependence of bias activated negative capacitance in\n  semiconductor diodes under high forward bias: We observed qualitatively dissimilar frequency dependence of negative\ncapacitive response under high charge injection in two sets of junction diodes\nwhich are functionally different from each other i.e. electroluminescent diodes\nand non-luminescent Si-based diodes. Using the technique of bias-activated\ndifferential capacitance response, we investigated the mutual dynamics of\ndifferent rate processes in different diodes. We explain these observations as\nthe mutual competition of fast and slow electronic transition rates albeit\ndifferently. This study provides a better understanding of the physics of\njunction diodes operating under high charge carrier injection and may lead to\nsuperior device functionalities.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Weak antilocalization beyond the fully diffusive regime in Pb1-xSnxSe\n  topological quantum wells: We report the measurements and analysis of weak antilocalization (WAL) in\nPb1-xSnxSe topological quantum wells in a new regime where the elastic\nscattering length is larger than the magnetic length. We achieve this regime\nthrough the development of high-quality epitaxy and doping of topological\ncrystalline insulator (TCI) quantum wells. We obtain elastic scattering lengths\nthat exceeds 100nm and become comparable to the magnetic length. In this\ntransport regime, the Hikami-Larkin-Nagaoka model is no longer valid. We employ\nthe model of Wittmann and Schmid to extract the coherence time from the\nmagnetoresistance. We find that despite our improved transport characteristics,\nthe coherence time may be limited by scattering channels that are not strongly\ncarrier dependent, such as electron-phonon or defect scattering.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Using single quantum states as spin filters to study spin polarization\n  in ferromagnets: By measuring electron tunneling between a ferromagnet and individual energy\nlevels in an aluminum quantum dot, we show how spin-resolved quantum states can\nbe used as filters to determine spin-dependent tunneling rates. We also observe\nmagnetic-field-dependent shifts in the magnet's electrochemical potential\nrelative to the dot's energy levels. The shifts vary between samples and are\ngenerally smaller than expected from the magnet's spin-polarized density of\nstates. We suggest that they are affected by field-dependent charge\nredistribution at the magnetic interface.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum properties of a strongly driven Josephson junction: A Josephson junction embedded in a dissipative circuit can be externally\ndriven to induce nonlinear dynamics of its phase. Classically, under\nsufficiently strong driving and weak damping, dynamic multi-stability emerges\nassociated with dynamical bifurcations so that the often used modeling as a\nDuffing oscillator, which can exhibit bi-stability at the most, is\ninsufficient. The present work analyzes in this regime corresponding quantum\nproperties by mapping the problem onto a highly-nonlinear quasi-energy operator\nin a rotating frame. This allows us to identify in detail parameter regions\nwhere simplifications such as the Duffing approximation are valid, to explore\nclassical-quantum correspondences, and to study how quantum fluctuations impact\nthe effective junction parameters as well as the dynamics around higher\namplitude classical fixed points.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Spatiotemporal spin fluctuations caused by spin-orbit-coupled Brownian\n  motion: We develop a theory of thermal fluctuations of spin density emerging in a\ntwo-dimensional electron gas. The spin fluctuations probed at spatially\nseparated spots of the sample are correlated due to Brownian motion of\nelectrons and spin-obit coupling. We calculate the spatiotemporal correlation\nfunctions of the spin density for both ballistic and diffusive transport of\nelectrons and analyze them for different types of spin-orbit interaction\nincluding the isotropic Rashba model and persistent spin helix regime. The\nmeasurement of spatial spin fluctuations provides direct access to the\nparameters of spin-orbit coupling and spin transport in conditions close to the\nthermal equilibrium.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Ab initio simulation of the structure and transport properties of\n  zirconium and ferromagnetic cobalt contacts on the two-dimensional\n  semiconductor WS_2: Using density-functional theory calculations, the atomic and electronic\nstructure of single-layer WS_2 attached to Zr and Co contacts are determined.\nBoth metals form stable interfaces that are promising as contacts for injection\nof n-type carriers into the conduction band of WS_2 with Schottky barriers of\n0.45eV and 0.62eV for Zr and Co, respectively. With the help of quantum\ntransport calculations, we address the conductive properties of a free-standing\nWS_2 sheet suspended between two Zr contacts. It is found that such a device\nbehaves like a diode with steep I-V characteristics. Spin-polarized transport\nis calculated for such a device with a floating-gate Co electrode added.\nDepending on the geometrical shape of the Co gate and the energy of the\ncarriers in WS_2, the transmission of spin majority and minority electrons may\ndiffer by up to an order of magnitude. Thus the steep I-V characteristics of\nthe nanoscale device makes it possible to realize a spin filter.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Large-Scale Schr\u00f6dinger-Cat States and Majorana Bound States in\n  Coupled Circuit-QED Systems: We have studied the low-lying excitations of a chain of coupled circuit-QED\nsystems, and report several intriguing properties of its two nearly degenerate\nground states. The ground states are Schr\\\"odinger cat states at a truly large\nscale, involving maximal entanglement between the resonator and the qubit, and\nare mathematically equivalent to Majorana bound states. With a suitable design\nof physical qubits, they are protected against local fluctuations and\nconstitute a non-local qubit. Further, they can be probed and manipulated\ncoherently by attaching an empty resonator to one end of the circuit-QED chain.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "High Mobility Free-Standing InSb Nanoflags Grown On InP Nanowire Stems\n  For Quantum Devices: High quality heteroepitaxial two-dimensional (2D) InSb layers are very\ndifficult to realize owing to the large lattice mismatch with other widespread\nsemiconductor substrates. A way around this problem is to grow free-standing 2D\nInSb nanostructures on nanowire (NW) stems, thanks to the capability of NWs to\nefficiently relax elastic strain along the sidewalls when lattice-mismatched\nsemiconductor systems are integrated. In this work, we optimize the morphology\nof free-standing 2D InSb nanoflags (NFs). In particular, robust NW stems,\noptimized growth parameters, and the use of reflection high-energy electron\ndiffraction (RHEED), to precisely orient the substrate for preferential growth,\nare implemented to increase the lateral size of the 2D InSb NFs. Transmission\nelectron microscopy (TEM) analysis of these NFs reveals defect-free zinc blend\ncrystal structure, stoichiometric composition, and relaxed lattice parameters.\nThe resulting NFs are large enough to fabricate Hall-bar contacts with suitable\nlength-to-width ratio enabling precise electrical characterization. An electron\nmobility of ~29,500 cm2/Vs is measured, which is the highest value reported for\nfree-standing 2D InSb nanostrutures in literature. We envision the use of 2D\nInSb NFs for fabrication of advanced quantum devices.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Thermally-Activated Phase Slips in Superfluid Spin Transport in Magnetic\n  Wires: We theoretically study thermally-activated phase slips in superfluid spin\ntransport in easy-plane magnetic wires within the stochastic\nLandau-Lifshitz-Gilbert phenomenology, which runs parallel to the\nLanger-Ambegaokar-McCumber-Halperin theory for thermal resistances in\nsuperconducting wires. To that end, we start by obtaining the exact solutions\nfor free-energy minima and saddle points. We provide an analytical expression\nfor the phase-slip rate in the zero spin-current limit, which involves detailed\nanalysis of spin fluctuations at extrema of the free energy. An experimental\nsetup of a magnetoeletric circuit is proposed, in which thermal phase slips can\nbe inferred by measuring nonlocal magnetoresistance.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Multiphoton excitation and high harmonic generation in rectangular\n  graphene quantum dot: The multiphoton excitation and high harmonic generation (HHG) processes are\nconsidered using the microscopic quantum theory of nonlinear interaction of\nstrong coherent electromagnetic (EM) radiation with rectangular graphene\nquantum dot (RGQD). The dynamic Hartree-Fock approximation is developed for the\nconsideration of the quantum dot-laser field nonlinear interaction at the\nnonadiabatic multiphoton excitation regime. The many-body Coulomb interaction\nis described in the extended Hubbard approximation. By numerical results, we\nshow the significance of the RGQD lateral size, shape, and EM wavefield\norientation in RGQD of the zigzag edge compear to the armchair edge in the HHG\nprocess allowing for increasing the cutoff photon energy and the quantum yield\nof higher harmonics.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Commensurate and incommensurate double moir\u00e9 interference in twisted\n  trilayer graphene: Twisted graphene multi-layers have been recently demonstrated to share\nseveral correlation-driven behaviours with twisted bilayer graphene. In\ngeneral, the van Hove singularities (VHSs) can be used as a proxy of the\ntendency for correlated behaviours. In this paper, we adopt an atomistic method\nby combining tight-binding method with the semi-classical molecular dynamics to\ninvestigate the electronic structures of twisted trilayer graphene (TTG) with\ntwo independent twist angles. The two independent twist angles can lead to the\ninterference of the moir\\'e patterns forming a variety of\ncommensurate/incommensurate complex supermoir\\'e patterns. In particular, the\nlattice relaxation, twist angle and angle disorder effects on the VHS are\ndiscussed. We find that the lattice relaxation significantly influence the\nposition and magnitude of the VHSs. In the supermoir\\'e TTG, the moir\\'e\ninterference provides constructive or destructive effects depending on the\nrelative twist angle. By modulating the two independent twist angles, novel\nsuperstructures, for instance, the Kagome-like lattice, could constructed via\nthe moir\\'e pattern. Moreover, we demonstrate that a slight change in twist\nangles (angle disorder) provides a significant suppression of the peak of the\nVHSs. Apart from the moir\\'e length, the evolution of the VHSs and the LDOS\nmapping in real space could be used to identify the twist angles in the\ncomplicated TTG. In practice, our work could provide a guide for exploring the\nflat band behaviours in the supermoir\\'e TTG experimentally.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Anisotropic 2D materials for tunable hyperbolic plasmonics: Motivated by the recent emergence of a new class of anisotropic 2D materials,\nwe examine their electromagnetic modes and demonstrate that a broad class of\nthe materials can host highly directional hyperbolic plasmons. Their\npropagation direction can be manipulated on-the-spot by gate doping, enabling\nhyperbolic beams reflection, refraction and bending. The realization of these\nnatural 2D hyperbolic media opens up a new avenue in dynamic control of\nhyperbolic plasmons not possible in the 3D version.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Resonant Coherent Phonon Generation in Single-Walled Carbon Nanotubes\n  through Near-Band-Edge Excitation: We have observed large-amplitude coherent phonon oscillations of radial\nbreathing modes (RBMs) in single-walled carbon nanotubes excited through the\nlowest-energy (E11) interband transitions. In contrast to the\npreviously-studied coherent phonons excited through higher-energy (E22)\ntransitions, these RBMs show comparable intensities between (n-m) mod 3 = 1 and\n-1 nanotubes. We also find novel non-resonantly excited RBMs over an excitation\nrange of ~300 meV above the E11 transition, which we attribute to multi-phonon\nreplicas arising from strong exciton-phonon coupling.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Quantum Hall Effect in a Graphene p-n Junction: We report on the fabrication and transport studies of a single-layer graphene\np-n junction. Carrier type and density in two adjacent regions are individually\ncontrolled by electrostatic gating using a local top gate and a global back\ngate. A functionalized Al203 oxide that adheres to graphene and does not\nsignificantly affect its electronic properties is described. Measurements in\nthe quantum Hall regime reveal new plateaus of two-terminal conductance across\nthe junction at 1 and 3/2 times the quantum of conductance, e2/h, consistent\nwith theory.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "The dynamical bulk boundary correspondence and dynamical quantum phase\n  transitions in the Benalcazar-Bernevig-Hughes model: In this article we demonstrate that dynamical quantum phase transitions occur\nfor an exemplary higher order topological insulator, the\nBenalcazar-Bernevig-Hughes model, following quenches across a topological phase\nboundary. A dynamical bulk boundary correspondence is also seen both in the\neigenvalues of the Loschmidt overlap matrix and the boundary return rate. The\nlatter is found from a finite size scaling analysis for which the relative\nsimplicity of the model is crucial. Contrary to the usual two dimensional case\nthe dynamical quantum phase transitions in this model show up as cusps in the\nreturn rate, as for a one dimensional model, rather than as cusps in its\nderivative as would be typical for a two dimensional model. We explain the\norigin of this behaviour.",
        "category": "cond-mat_mes-hall"
    },
    {
        "text": "Robust Type-II Weyl Semimetal Phase in Transition Metal Diphosphides\n  XP$_2$ (X = Mo, W): The recently discovered type-II Weyl points appear at the boundary between\nelectron and hole pockets. Type-II Weyl semimetals that host such points are\npredicted to exhibit a new type of chiral anomaly and possess thermodynamic\nproperties very different from their type-I counterparts. In this Letter, we\ndescribe the prediction of a type-II Weyl semimetal phase in the transition\nmetal diphosphides MoP$_2$ and WP$_2$. These materials are characterized by\nrelatively simple band structures with four pairs of type-II Weyl points.\nNeighboring Weyl points have the same chirality, which makes the predicted\ntopological phase robust with respect to small perturbations of the crystalline\nlattice. In addition, this peculiar arrangement of the Weyl points results in\nlong topological Fermi arcs, thus making them readily accessible in\nangle-resolved photoemission spectroscopy.",
        "category": "cond-mat_mes-hall"
    }
]